Novel dyes and use thereof in imaging members and methods

ABSTRACT

There are described novel rhodamine dye compounds and imaging members and imaging methods, including thermal imaging members and imaging methods, utilizing the compounds. The dye compounds exhibit a first color when in the crystalline form and a second color, different from the first color, when in the liquid, amorphous form.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending U.S. patent application Ser. No. 11/751,286, filed on May 21, 2007, entitled “Process for the Preparation of Novel Dyes for use in Imaging Systems”, which is a continuation of U.S. patent application Ser. No. 11/369,805 filed on Mar. 6, 2006, now U.S. Pat. No. 7,220,868, which is a continuation of U.S. patent application Ser. No. 10/788,963 filed on Feb. 27, 2004, now U.S. Pat. No. 7,008,759, which claims priority from Provisional Application No. 60/451,208, filed on Feb. 28, 2003. This application is also a continuation-in-part of U.S. patent application Ser. No. 11/433,808, filed May 12, 2006, entitled “Thermal Imaging Members and Methods”, which claims the benefit of priority from U.S. Provisional Application No. 60/680,088, filed May 12, 2005 and 60/680,212, filed on May 12, 2005. The contents of the above-referenced applications are incorporated herein by reference in their entireties.

This application also related to the following commonly assigned United States patent applications and patents, the disclosures of all of which are hereby incorporated by reference herein in their entirety:

U.S. Pat. No. 6,801,233 B2 which describes and claims a thermal imaging system for use in the present invention;

U.S. Pat. No. 7,008,759 B2 which describes and claims color-forming compositions for use in the present invention;

U.S. Pat. No. 7,176,161 B2 which describes and claims color-forming compositions for use in the present invention;

U.S. Pat. No. 7,282,317 B2 which describes and claims color-forming compositions for use in the present invention;

U.S. patent application Ser. No. 11/400734, filed Apr. 6, 2006, which describes and claims an imaging method for use in the present invention; and

U.S. patent application Ser. No. 11/400735, filed Apr. 6, 2006, which describes and claims an imaging method for use in the present invention; and

U.S. patent application Ser. No. 11/433808, filed May 12, 2006, entitled “Thermal Imaging Members and Methods”.

FIELD OF THE INVENTION

This invention relates to novel compounds and, more particularly, to compounds which exhibit one color in the crystalline form and a second, different color in the liquid, or amorphous, form. Also described are imaging members and methods, including thermal imaging members and methods, utilizing the compounds.

BACKGROUND OF THE INVENTION

The development of thermal print heads (linear arrays of individually-addressable resistors) has led to the development of a wide variety of thermally-sensitive media. In some of these, known as “thermal transfer” systems, heat is used to move colored material from a donor sheet to a receiver sheet. Alternatively, heat may be used to convert a colorless coating on a single sheet into a colored image, in a process known as “direct thermal” imaging. Direct thermal imaging has the advantage over thermal transfer of the simplicity of a single sheet. On the other hand, unless a fixing step is incorporated, direct thermal systems are still sensitive to heat after thermal printing. If a stable image is needed from an unfixed direct thermal system, the temperature for coloration must be higher than any temperature that the image is likely to encounter during normal use. A problem arises in that the higher the temperature for coloration, the less sensitive the medium will be when printed with the thermal print head. High sensitivity is important for maximum speed of printing, for maximizing the longevity of the print head, and for energy conservation in mobile, battery-powered printers. As described in more detail below, maximizing sensitivity while maintaining stability is more easily achieved if the temperature of coloration of a direct thermal medium is substantially independent of the heating time.

Thermal print heads address one line of the image at a time. For reasonable printing times, each line of the image is heated for about ten milliseconds or less. Storage of the medium (prior to printing or in the form of the final image) may need to be for years, however. Thus, for high imaging sensitivity, a high degree of coloration is required in a short time of heating, while for good stability a low degree of coloration is required for a long time of heating.

Most chemical reactions speed up with increasing temperature. Therefore, the temperature required for coloration in the short heating time available from a thermal print head will normally be higher than the temperature needed to cause coloration during the long storage time. Actually reversing this order of temperatures would be a very difficult task, but maintaining a substantially time-independent temperature of coloration, such that both long-time and short-time temperatures for coloration are substantially the same, is a desirable goal that is achieved by the present invention.

There are other reasons why a time-independent coloration temperature may be desirable. It may, for example, be required to perform a second thermal step, requiring a relatively long time of heating, after printing. An example of such a step would be thermal lamination of an image. The temperature of coloration of the medium during the time required for thermal lamination must be higher than the lamination temperature (otherwise the medium would become colorized during lamination). It would be preferred that the imaging temperature be higher than the lamination temperature by as small a margin as possible, as would be the case for time-independent temperature of coloration.

Finally, the imaging system may comprise more than one color-forming layer and be designed to be printed with a single thermal print-head, as described in the above-mentioned patent application Ser. No. 10/151,432. In one embodiment of the imaging system, the topmost color-forming layer forms color in a relatively short time at a relatively high temperature, while the lower layer or layers form color in a relatively long time at a relatively low temperature. An ideal topmost layer for this type of direct thermal imaging system would have time-independent temperature of coloration.

Prior art direct thermal imaging systems have used several different chemical mechanisms to produce a change in color. Some have employed compounds that are intrinsically unstable, and which decompose to form a visible color when heated. Such color changes may involve a unimolecular chemical reaction. This reaction may cause color to be formed from a colorless precursor, the color of a colored material to change, or a colored material to bleach. The rate of the reaction is accelerated by heat. For example, U.S. Pat. No. 3,488,705 discloses thermally unstable organic acid salts of triarylmethane dyes that are decomposed and bleached upon heating. U.S. Pat. No. 3,745,009 reissued as U.S. Reissue Pat. No. 29,168 and U.S. Pat. No. 3,832,212 disclose heat-sensitive compounds for thermography containing a heterocyclic nitrogen atom substituted with an —OR group, for example, a carbonate group, that decolorize by undergoing homolytic or heterolytic cleavage of the nitrogen-oxygen bond upon heating to produce an RO+ ion or RO′ radical and a dye base or dye radical which may in part fragment further. U.S. Pat. No. 4,380,629 discloses styryl-like compounds that undergo coloration or bleaching, reversibly or irreversibly, via ring-opening and ring-closing in response to activating energies. U.S. Pat. No. 4,720,449 describes an intramolecular acylation reaction that converts a colorless molecule to a colored form. U.S. Pat. No. 4,243,052 describes pyrolysis of a mixed carbonate of a quinophthalone precursor that may be used to form a dye. U.S. Pat. No. 4,602,263 describes a thermally-removable protecting group that may be used to reveal a dye or to change the color of a dye. U.S. Pat. No. 5,350,870 describes an intramolecular acylation reaction that may be used to induce a color change. A further example of a unimolecular color-forming reaction is described in “New Thermo-Response Dyes: Coloration by the Claisen Rearrangement and Intramolecular Acid-Base Reaction Masahiko Inouye, Kikuo Tsuchiya, and Teijiro Kitao, Angew. Chem. Int. Ed. Engl. 31, pp. 204-5 (1992).

In all of the above-mentioned examples, control of the chemical reaction is achieved through the change in rate that occurs with changing temperature. Thermally-induced changes in rates of chemical reactions in the absence of phase changes may often be approximated by the Arrhenius equation, in which the rate constant increases exponentially as the reciprocal of absolute temperature decreases (i.e., as temperature increases). The slope of the straight line relating the logarithm of the rate constant to the reciprocal of the absolute temperature is proportional to the so-called “activation energy”. The prior art compounds described above are coated in an amorphous state prior to imaging, and thus no change in phase is expected or described as occurring between room temperature and the imaging temperature. Thus, as employed in the prior art, these compounds exhibit strongly time-dependent coloration temperatures. Some of these prior art compounds are described as having been isolated in crystalline form. Nevertheless, in no case is there mentioned in this prior art any change in activation energy of the color-forming reaction that may occur when crystals of the compounds are melted.

Other prior art thermal imaging media depend upon melting to trigger image formation. Typically, two or more chemical compounds that react together to produce a color change are coated onto a substrate in such a way that they are segregated from one another, for example, as dispersions of small crystals. Melting, either of the compounds themselves or of an additional fusible vehicle, brings them into contact with one another and causes a visible image to be formed. For example, a colorless dye precursor may form color upon heat-induced contact with a reagent. This reagent may be a Bronsted acid, as described in “Imaging Processes and Materials”, Neblette's Eighth Edition, J. Sturge, V. Walworth, A. Shepp, Eds., Van Nostrand Reinhold, 1989, pp. 274-275, or a Lewis acid, as described for example in U.S. Pat. No. 4,636,819. Suitable dye precursors for use with acidic reagents are described, for example, in U.S. Pat. No. 2,417,897, South African Patent 68-00170, South African Patent 68-00323 and Ger. Off enlegungschrift 2,259,409. Further examples of such dyes may be found in “Synthesis and Properties of Phthalide-type Color Formers”, by In a Fletcher and Rudolf Zink, in “Chemistry and Applications of Leuco Dyes”, Muthyala Ed., Plenum Press, New York, 1997. The acidic material may for example be a phenol derivative or an aromatic carboxylic acid derivative. Such thermal imaging materials and various combinations thereof are now well known, and various methods of preparing heat-sensitive recording elements employing these materials also are well known and have been described, for example, in U.S. Pat. Nos. 3,539,375, 4,401,717 and 4,415,633. U.S. Pat. Nos. 4,390,616 and 4,436,920 describe image forming members comprising materials similar to those of the present invention. The materials described therein are fluoran dyes for use in conjunction with a developer, and there is not report of image formation upon melting in the absence of a developer.

Prior art systems in which at least two separate components are mixed following a melting transition suffer from the drawback that the temperature required to form an image in a very short time by a thermal print-head may be substantially higher than the temperature required to colorize the medium during longer periods of heating. This difference is caused by the change in the rate of the diffusion needed to mix the molten components together, which may become limiting when heat is applied for very short periods. The temperature may need to be raised well above the melting points of the individual components to overcome this slow rate of diffusion. Diffusion rates may not be limiting during long periods of heating, however, and the temperature at which coloration takes place in these cases may actually be less than the melting point of either individual component, occurring at the eutectic melting point of the mixture of crystalline materials.

As the state of the art in imaging systems advances and efforts are made to provide new imaging systems that can meet new performance requirements, and to reduce or eliminate some of the undesirable characteristics of the known systems, it would be advantageous to have new compounds which can be used as image-forming materials in imaging systems, including thermal imaging systems.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide novel compounds.

Another object of the invention is to provide compounds which exhibit different colors when in the crystalline form and in the liquid form.

Yet another object of the invention is to provide imaging members and methods, including thermal imaging members and methods, which utilize the novel compounds.

The present invention provides novel rhodamine compounds that are useful as image dyes in imaging systems. According to one aspect of the invention there are provided novel dye compounds which exhibit a first color when in the crystalline form and a second color, different from the first color, when in the liquid, amorphous form.

In one embodiment of the invention there are provided novel compounds which are represented by formula I

wherein:

R₁, R₃, R₄, R₅, R₆ and R₇ are each independently selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted, alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, halogen, nitro, nitrilo, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, oxygen, substituted oxygen, nitrogen, substituted nitrogen, sulfur and substituted sulfur;

R₂ is selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, substituted oxygen, substituted nitrogen and substituted sulfur;

R₈ is absent or selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, halogen, nitro, nitrilo, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, oxygen, substituted oxygen, nitrogen, substituted nitrogen, sulfur and substituted sulfur;

R₉, R₁₀ and R₁₁ are independently selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, halogen, nitro, nitrilo, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, oxygen, substituted oxygen, nitrogen, substituted nitrogen, sulfur and substituted sulfur;

R₁₂, R₁₃, R₁₄ and R₁₅ are independently selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, aryl, substituted aryl, heteroaryl, and substituted heteroaryl;

R₁₆, R₁₇, R₁₈ and R₁₉ are independently selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, halogen, nitro, nitrilo, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, oxygen, substituted oxygen, nitrogen, substituted nitrogen, sulfur and substituted sulfur; and X₁ is carbon or nitrogen.

In a preferred group of compounds represented by formula I, R₈, R₉, R₁₀ and R₁₁ are halogen and R₁, R₂, R₃, R₄, R₅, R₅, R₇, R₁₂, R₁₃, R₁₄, R₁₅, R₁₆, R₁₇, R₁₈ and R₁₉ are as previously defined and X₁ is carbon.

The conversion to the liquid form can be carried out by applying heat to the compounds and therefore the compounds are useful in thermal imaging members used in thermal imaging methods. In such thermal imaging methods thermal energy may be applied to the thermal imaging members by any of the techniques known in thermal imaging such as from a thermal print head, a laser, a heated stylus, etc. In another embodiment, the conversion to the liquid form may be effected by applying a solvent for the crystalline solid such as from an ink jet imaging apparatus to at least partially dissolve the crystalline material. In another embodiment, one or more thermal solvents, which are crystalline materials, can be incorporated in the thermal imaging member. The crystalline thermal solvent(s), upon being heated, melt and dissolve or liquefy, and thereby convert, at least partially, the crystalline image-forming material to the liquid amorphous form to form the image.

The compounds of the invention may be incorporated in any suitable thermal imaging members. Typical suitable thermal imaging members generally comprise a substrate carrying at least one image-forming layer including a compound in the crystalline form, which can be converted, at least partially to a liquid in the amorphous form, the liquid having intrinsically a different color from the crystalline form. The thermal imaging member may be monochrome or multicolor and the temperature at which an image is formed in at least one of the image-forming layers is time independent.

Preferred thermal imaging members according to the invention are those having the structures described in prior co-pending commonly assigned U.S. patent application Ser. No. 09/745,700 filed Dec. 20, 2000, now U.S. Pat. No. 6,537,410 B1 which is hereby incorporated herein by reference in its entirety and made a part of this application.

Other preferred thermal imaging members are those having the structures described in prior, co-pending commonly assigned U.S. patent application Ser. No. 10/151,432 filed May 20, 2002 which is hereby incorporated herein by reference in its entirety and made a part of this application.

Further preferred thermal imaging members are those having the structures described in U.S. Pat. No. 6,054,246 which is hereby incorporated herein by reference in its entirety and made a part of this application.

DETAILED DESCRIPTION OF THE INVENTION

Compounds in the crystalline state commonly have properties, including color, that are very different from those of the same compounds in an amorphous form. In a crystal, a molecule is typically held in a single conformation (or, more rarely, in a small number of conformations) by the packing forces of the lattice. Likewise, if a molecule can exist in more than one interconverting isomeric forms, only one of such isomeric forms is commonly present in the crystalline state. In amorphous form or solution, on the other hand, the compound may explore its whole conformational and isomeric space, and only a small proportion of the population of individual molecules of the compound may at any one time exhibit the particular conformation or isomeric form adopted in the crystal. Compounds of the present invention exhibit tautomerism in which at least one tautomeric form is colorless, and at least another tautomeric form is colored. The crystalline form of compounds of the present invention comprises predominantly the colorless tautomer.

A first embodiment of the invention is a compound represented by Formula I as described above.

A first embodiment of the invention is a compound whose colorless tautomer is represented by formula I as described above.

Representative compounds according to the invention are those of formula I in which R₁, R₃, R₄, R₅, R₆, R₇, R₁₂, R₁₆ , R₁₈ and R₁₉ are hydrogen, X₁ is carbon, and the other substituents are as shown in Table I:

TABLE I Com- R₈, R₉, R₁₃, pound R₂ R₁₀, R₁₁ R₁₄, R₁₅ R₁₇ I C₆H₅ Cl Me H II 4-(O-2-ethyl-1-hexyl)C₆H₄ Cl H H III 3,4-dioctyloxy-C₆H₃ Cl H H IV 4-(2-hydroxy-1-decyloxy)-C₆H₄ Cl H H V 3,4-dioctyloxy-C₆H₃ Cl H OMe VI 2-isopropyl-C₆H₄ F H H VII 2-Methyl-4-decyloxy-C₆H₃ F H H VIII 2-Methyl-4-decyloxy-C₆H₃ F H Me IX 2-Methyl-4-octadecyloxy-C₆H₃ F H H

Preferred compounds according to the invention are III, VII and VIII.

Definitions

The term “alkyl” as used herein refers to saturated straight-chain, branched-chain or cyclic hydrocarbon radicals. Examples of alkyl radicals include, but are not limited to, methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, neopentyl, n-hexyl, cyclohexyl, n-octyl, n-decyl, n-dodecyl and n-hexadecyl radicals.

The term “alkenyl” as used herein refers to unsaturated straight-chain, branched-chain or cyclic hydrocarbon radicals. Examples of alkenyl radicals include, but are not limited to, allyl, butenyl, hexenyl and cyclohexenyl radicals.

The term “alkynyl” as used herein refers to unsaturated hydrocarbon radicals having at least one carbon-carbon triple bond. Representative alkynyl groups include, but are not limited to, ethynyl, 1-propynyl, 1-butynyl, isopentynyl, 1,3-hexadiynyl, n-hexynyl, 3-pentynyl, 1-hexen-3-ynyl and the like.

The terms “halo” and “halogen,” as used herein, refer to an atom selected from fluorine, chlorine, bromine and iodine.

The term “aryl,” as used herein, refers to a mono-, bicyclic or tricyclic carbocyclic ring system having one, two or three aromatic rings including, but not limited to, phenyl, naphthyl, anthryl, azulyl, tetrahydronaphthyl, indanyl, indenyl and the like.

The term “heteroaryl,” as used herein, refers to a cyclic aromatic radical having from five to ten ring atoms of which one ring atom is selected from S, O and N; zero, one or two ring atoms are additional heteroatoms independently selected from S, O and N; and the remaining ring atoms are carbon, the radical being joined to the rest of the molecule via any of the ring atoms, such as, for example, pyridinyl, pyrazinyl, pyrimidinyl, pyrrolyl, pyrazolyl, imidazolyl, thiazolyl, oxazolyl, isooxazolyl, thiadiazolyl, oxadiazolyl, thiophenyl, furanyl, quinolinyl, isoquinolinyl, and the like.

The term “heterocycloalkyl,” as used herein, refers to a non-aromatic 3-, 4-, 5-, 6- or 7-membered ring or a bi- or tri-cyclic group comprising fused six-membered rings having between one and three heteroatoms independently selected from oxygen, sulfur and nitrogen, wherein (i) each 5-membered ring has 0 to 1 double bonds and each 6-membered ring has 0 to 2 double bonds, (ii) the nitrogen and sulfur heteroatoms may optionally be oxidized, (iii) the nitrogen heteroatom may optionally be quaternized, and (iv) any of the above heterocyclic rings may be fused to a benzene ring. Representative heterocycles include, but are not limited to, pyrrolidinyl, pyrazolinyl, pyrazolidinyl, imidazolinyl, imidazolidinyl, piperidinyl, piperazinyl, oxazolidinyl, isoxazolidinyl, morpholinyl, thiazolidinyl, isothiazolidinyl, and tetrahydrofuryl.

The term “carbonyl” as used herein refers to a carbonyl group, attached to the parent molecular moiety through the carbon atom, this carbon atom also bearing a hydrogen atom, or in the case of a “substituted carbonyl” a substituent as described in the definition of “substituted” below.

The term “acyl” as used herein refers to groups containing a carbonyl moiety. Examples of acyl radicals include, but are not limited to, formyl, acetyl, propionyl, benzoyl and naphthyl.

The term “alkoxy”, as used herein, refers to a substituted or unsubstituted alkyl, alkenyl or heterocycloalkyl group, as previously defined, attached to the parent molecular moiety through an oxygen atom. Examples of alkoxy radicals include, but are not limited to, methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, tert-butoxy, neopentoxy and n-hexoxy.

The term ‘aryloxy” as used herein refers to a substituted or unsubstituted aryl or heteroaryl group, as previously defined, attached to the parent molecular moiety through an oxygen atom. Examples of aryloxy include, but are not limited to, phenoxy, p-methylphenoxy, naphthoxy and the like.

The term “alkylamino”, as used herein, refers to a substituted or unsubstituted alkyl, alkenyl or heterocycloalkyl group, as previously defined, attached to the parent molecular moiety through a nitrogen atom. Examples of alkylamino radicals include, but are not limited to, methylamino, ethylamino, hexylaminoand dodecylamino.

The term “arylamino”, as used herein, refers to a substituted or unsubstituted aryl or heteroaryl group, as previously defined, attached to the parent molecular moiety through a nitrogen atom.

The term “substituted” as used herein in phrases such as “substituted alkyl”, “substituted alkenyl”, “substituted aryl”, “substituted heteroaryl”, “substituted heterocycloalkyl”, “substituted carbonyl”, “substituted alkoxy”, “substituted acyl”, “substituted amino”, “substituted aryloxy”, and the like, refers to independent replacement of one or more of the hydrogen atoms on the substituted moiety with substituents independently selected from, but not limited to, alkyl, alkenyl, heterocycloalkyl, alkoxy, aryloxy, hydroxy, amino, alkylamino, arylamino, cyano, halo, mercapto, nitro, carbonyl, acyl, aryl and heteroaryl groups.

According to the invention, there have been provided molecules exhibiting tautomerism in which at least one tautomeric form is colorless, and at least another tautomeric form is colored. Crystallization of the equilibrating mixture of the two tautomeric forms is carried out so as to produce colorless crystals. The solvent chosen to perform the crystallization will typically be one of such polarity (and other chemical properties, such as hydrogen-bonding ability) that the pure colorless crystal form is favored, either in the equilibrium between the colorless and colored forms in solution, or in having lower solubility in the solvent than the colored form. The choice of solvent is usually determined empirically for a particular mixture of tautomers.

Upon conversion of the pure crystalline colorless form, the equilibrium between the two tautomers is re-established in the resulting amorphous (liquid) phase. The proportion of the amorphous material that is colored (i.e., the proportion that is in the colored tautomeric form) may vary, but is preferably at least about 10%.

The colored and colorless tautomeric forms of the molecules of the present invention must meet certain criteria for image quality and permanence. The colorless form, which is preferably the crystalline form, should have minimal visible absorption. It should be stable to light, heating below the melting point, humidity, and other environmental factors such as ozone, oxygen, nitrogen oxides, fingerprint oils, etc. These environmental factors are well known to those skilled in the imaging art. The colored, amorphous form should be stable also to the above mentioned conditions, and in addition should not recrystallize to the colorless form under normal handling conditions of the image. The colored form should have a spectral absorption appropriate for digital color rendition. Typically, the colored form should be yellow (blue-absorbing), magenta (green-absorbing), cyan (red absorbing), or black, without undue absorption in an unintended spectral region. For nonphotographic applications, however, it may be required that the colored form not be one of the subtractive primary colors, but rather a particular spot color (for example, orange, blue, etc.).

The compounds of the invention may be prepared by synthetic processes which are known to those skilled in the art, particularly in view of the state of the art and the specific preparatory examples provided below herein.

Symmetrical rhodamine dyes can be prepared in one step from 3′,6′-dichlorofluorans by reacting two equivalents of an aromatic or aliphatic amine as described in U.S. Pat. No. 4,602,263, British Patent No. GB2311075 and German Patent No. DE81056. The novel unsymmetrical rhodamine dyes in this application require a more controlled synthetic pathway in which one equivalent of an indoline is reacted selectively with the 3′,6′-dichlorofluoran using aluminum chloride as a catalyst to produce 3′-chloro-6′-indolinofluorans. These products are isolated and purified prior to reacting with a second equivalent of an aromatic or aliphatic amine. Zinc chloride is used as the catalyst for the second addition. German Patent No. DE139727 describes the selective addition of anilines to 3′,6′-dichlorofluorans to produce 3′-chloro-6′-arylaminofluorans using a mixture of zinc chloride and zinc oxide at 160° C.

To optimize the chromophore, melting point, degree of coloration, light stability and solubility of the dyes in this application a variety of indolines, anilines and dichlorofluorans are utilized.

5-methoxyindoline and 5-methylindoline are prepared from the corresponding indoles by reduction with sodium cyanoborohydride in acetic acid. 2,3,3-trimethylindoline is prepared from 2,3,3-trimethylindolenine by hydrogenation.

The aromatic amines used in this application are synthesized from 4-nitro-3-methylphenol, 4-nitrophenol and 4-nitrocatechol. The anions of the phenols are generated in dimethylformamide with potassium carbonate and alkylated with a variety of alkylating agents such as 1-bromodecane, 1-bromooctadecane, 1-bromo-2-ethylhexane. Alternatively, the sodium salts of the phenols are alkylated with 1,2-epoxyalkanes using tetrabutylammonium sulfate in a boiling mixture of toluene and water. The resulting 4-nitrophenylethers are reduced to the corresponding anilines using standard methods such as hydrogenation, iron powder, hydrazine or ammonium formate.

The 3′,6′-dichlorofluorans are synthesized from the corresponding fluoresceins using thionyl chloride and dimethylformamide in a variation of the method of Hurd described in the Journal of the Amer. Chemical Soc. 59, 112 (1937). 4,5,6,7-tetrafluorofluorescein is prepared according to the procedure of Haugland described in the Journal of Organic Chemistry, 62, 6469 (1997).

The thermal imaging members of the invention can be direct thermal imaging members wherein an image is formed in the member itself or they can be thermal transfer imaging members whereby image-forming material is transferred to an image-receiving member. The melting point of the molecules used in direct thermal imaging members of the present invention is preferably in the range of about 60° C. to about 300° C. Melting points lower than about 60° C. lead to direct thermal imaging members that are unstable to temperatures occasionally encountered during handling of the members before or after imaging, while melting temperatures above about 300° C. render the compounds difficult to colorize with a conventional thermal print head. It should be noted, however, that there are uses for certain novel compounds of the present invention that do not require the use of thermal print heads (for example, laser imaging).

The colors formed by preferred compounds of the present invention are typically cyan, which is to say that the maximum absorption of the preferred compounds in the amorphous state lies between about 600 and about 700 nm. It has been found that the wavelength of maximum absorption of the colored form of compounds of the present invention is longer when substituents R₈, R₉, R₁₀ and R₁₁ of formula I are electron-withdrawing relative to hydrogen. Dyes with relatively short maximum absorption wavelengths may appear blue, rather than cyan, and for this reason substituents R₈, R₉, R₁₀ and R₁₁ of formula I are preferred to be highly electron-withdrawing, and preferably halogen, when X₁ of formula I is a carbon atom and the color cyan is desired.

To form a direct thermal imaging system, the crystalline, colorless form of the compounds of the invention is made into a dispersion in a solvent in which the compound is insoluble or only sparingly soluble, by any of the methods known in the art for forming dispersions. Such methods include grinding, attriting, etc. The particular solvent chosen will depend upon the particular crystalline material. Solvents that may be used include water, organic solvents such as hydrocarbons, esters, alcohols, ketones, nitriles, and organic halide solvents such as chlorinated and fluorinated hydrocarbons. The dispersed crystalline material may be combined with a binder, which may be polymeric. Suitable binders include water-soluble polymers such as poly(vinyl alcohol), poly(vinylpyrollidone) and cellulose derivatives, water-dispersed latices such as styrene/butadiene or poly(urethane) derivatives, or alternatively hydrocarbon-soluble polymers such as polyethylene, polypropylene, copolymers of ethylene and norbornene, and polystyrene. This list is not intended to be exhaustive, but is merely intended to indicate the breadth of choice available for the polymeric binder. The binder may be dissolved or dispersed in the solvent.

Following preparation of the dispersion of the compound of the present invention, and optional addition of a polymeric binder, the resultant fluid is coated onto a substrate using any of the techniques well-known in the coating art. These include slot, gravure, Meyer rod, roll, cascade, spray, and curtain coating techniques. The image-forming layer so formed is optionally overcoated with a protective layer or layers.

If materials of the present invention are used to prepare an imaging medium of the type described in copending U.S. patent application Ser. No. 10/151,432 filed May 20, 2002 the process described above is followed for each of the imaging layers. Successive layers may be coated sequentially, in tandem, or in a combination of sequential and tandem coatings.

EXAMPLES

The invention will now be described further in detail with respect to specific embodiments by way of examples, it being understood that these are intended to be illustrative only and the invention is not limited to the materials, amounts, procedures and process parameters, etc. recited therein. All parts and percentages recited are by weight unless otherwise specified.

Example 1 Synthesis of Intermediates

Step 1A. Alkylation of 4-nitrocatechol 4-Nitrocatechol (23.26 g, 0.15 mol) and potassium carbonate (124.38 g, 0.9 mol) were placed in a one liter 3-neck flask fitted with a mechanical stirrer. Anhydrous dimethylformamide (350 mL) was added to this mixture followed by the addition to the suspension, dropwise, of 1-bromo octane (63.73 g, 0.33 mol). The reaction mixture was heated at 110° C. for 24 hours. The reaction was followed by TLC (2% methanol in methylene chloride). After the completion of the reaction the contents were cooled and poured dropwise with stirring into ice-water (1 L). The mixture was stirred for one hour and filtered. The collected solid was washed thoroughly with water, air-dried and then dried in vacuo at 30° C. This process produced brown crystals: (54.8 g, 0.144 mol, 96% yield). These crystals were used without further purification.

Step 1B. Synthesis of 3,4-dioctyloxyaniline

3,4-Dioctyloxynitrobenzene (25.25 g, 0.067 mol) was dissolved in ethyl acetate (250 mL) in a Parr bottle. 10% Pd on charcoal (3.5 g) was added and the mixture was hydrogenated (5-6 hr) at 50 psi until the hydrogen uptake ceased. The reaction mixture was filtered and evaporated. The aniline was obtained as a dark syrup. (22.5 g, 0.064 mol, 97% yield). The structure was corroborated by NMR and mass spectroscopy.

Step 1C. Synthesis of 2-methyl-4-decyloxynitro benzene

To a solution of 3-methyl-4-nitrophenol (45 g, 0.294 mol) in dimethylformamide (270 mL) there were added 1-bromodecane (65 g, 0.294 mol) and potassium carbonate (121.8 g, 0.882 mol). The reaction mixture was heated to 115° C. and stirred at that temperature for 48 hours. The reaction mixture was cooled and poured into water (4 L), stirred for 0.5 hour and extracted with two portions of ethyl acetate (1.5 L and 600 mL). The combined organic extracts were washed with 5% aqueous solution sodium bicarbonate (1 L), water (1 L and 0.5 L), dried over sodium sulfate and concentrated to give the crude product (90 g, 0.294 mol, 100% yield). This product was used in the next step without purification.

Step 1D. Synthesis of 2-methyl-4-decyloxyaniline

The mixture of crude 2-methyl-4-decyloxynitrobenzene (90 g, 0.294 mol ), methanol (246 mL), concentrated hydrochloric acid (159 mL) and dioxane (70 mL) was heated to 75° C. Iron powder (49.9 g, 0.89 mol) was added in small portions with vigorous stirring. After the addition was complete the reaction mixture was stirred at 75° C. for another 20 minutes and poured warm into water (3 L), stirred for 30 minutes and the pH adjusted to 11.0 by addition of aqueous potassium carbonate solution. Dichloromethane (3 L) was added and the mixture was stirred intensively for 1 hour. The layers were separated and the organic layer dried over sodium sulfate and passed through a thin pad of silica gel. The solvent was evaporated to dryness to give a brown oil (58.5 g, 0.22 mol, 76% yield).

Step 1E. Synthesis of 2-methyl-4-octadecyloxynitrobenzene:

1-Bromooctadecane (43.54 g, 0.131 mol) and potassium carbonate (54.15 g, 0.392 mol) were added to a solution of 3-methyl-4-nitrophenol (20 g, 0.131 mol) in dimethylformamide (120 mL) The reaction mixture was heated to 110° C. and stirred at this temperature for 60 hours. The reaction mixture was cooled and poured into water (2 L), stirred for 0.5 hour and extracted with methylene chloride (1 L). The organic extract was washed with 5% aqueous solution sodium bicarbonate (0.5 L), water (2×0.6 L), dried over sodium sulfate and concentrated to give (60 g) of crude product. This product was used in the next step without purification.

Step 1F. Synthesis of 2-methyl-4-octadecyloxyaniline

The mixture of crude 2-methyl-4-octadecyloxynitrobenzene (30 g, ca. 0.065 mol), methanol (55 mL), concentrated hydrochloric acid (40.5 mL) and dioxane (50 mL) was heated to 85° C. Iron powder (11.2 g, 0.20 mol) was added in small portions with intensive stirring. After the addition was complete the reaction mixture was stirred at 85° C. for another 3 hours and poured warm into water (800 mL), stirred for 30 minutes and the pH adjusted to 10.0 by addition of aqueous potassium carbonate solution. Dichloromethane (1.0 L) was added and mixture was stirred intensively for 1 hour. The layers were separated and the organic layer was washed with water (2×500 mL) and dried over sodium sulfate. The solvent was evaporated to give an oil (20 g, 0.053 mol, 82% yield), which solidified on standing. The structure of this material was corroborated by proton NMR and mass spectroscopy.

Step 1G. Synthesis of 2-ethyl-1-hexyloxynitro benzene

4-Nitrophenol (10 g, 72 mmol) and potassium carbonate (30.4 g, 0.22 mol) were added to dimethylformamide (80 mL) at room temperature and the mixture was stirred with heating at 100° C. for 2 hours. 2-Ethyl-1-hexyl bromide (16.7 g, 86 mmol) was slowly added to the mixture for 20 minutes. After the addition the mixture was further stirred at 150° C. for 3 hours. After cooling, the reaction mixture was poured into water (500 mL) and then the mixture was extracted with methylene chloride. After evaporation of solvent, the residual product was isolated as an oil in high yield (18 g, 71.6 mmol, 99%

Step 1H. Synthesis of 2-ethyl-1-hexyloxy aniline

2-Ethyl-1-hexyloxynitro benzene (18 g, 72 mmol) was dissolved in isopropanol (80 mL) and 10% Pd/C (1 g) was slowly added to the mixture in a Parr pressure bottle. The mixture was hydrogenated at 40 psi for 5 hours and the mixture was filtered to remove Pd/C followed by evaporation of the solvent to give the oily product in quantitative yield (15.9 g, 72 mmol, 100% yield).

Step 1I. Synthesis of 4-(2-hydroxy-1-decyloxy)nitrobenzene

The sodium salt of 4-nitrophenol (28.19 g, 0.175 mol) was dissolved in water (50 mL) and toluene (300 mL) and tetrabutylammonium sulfate (6.0 g) was added. 1,2-Epoxydecane (27.3 g, 0.175 mol) was added to this mixture and the reaction was heated at 100° C. for 5 days. The toluene layer was separated and washed with water (4×75 mL), 1N hydrochloric acid (2×75 mL) and water (75 mL). The organic layer was dried over sodium sulfate, filtered and the solvent removed. The crude product was purified by silica gel chromatography (2-3% methanol/methylene chloride) to afford 4-(2-hydroxy-1-decyloxy)nitrobenzene as a pale oil (20 g, 0.68 mol, 39% yield).

Step 1J. Synthesis of 4-(2-hydroxy-1-decyloxy)aniline

4-(2-hydroxy-1-decyloxy)nitrobenzene (20 g, 0.68 mol) was dissolved in ethyl acetate (200 mL) and 10% palladium on carbon (2.5 g) was added to a Parr pressure bottle. The contents were then hydrogenated at 50 psi until hydrogen uptake ceased. The catalyst was removed by suction filtration through a pad of Celite. Removal of solvent afforded 4-(2-hydroxy-1-decyloxy)aniline in quantitative yield (18.0 g, 0.68 mol, 100% yield) as a tan solid. The structure was confirmed by NMR and mass spectroscopy.

Step 1K. Synthesis of 5-methoxyindoline

5-Methoxyindole (50 g, 0.34 mol) was dissolved in glacial acetic acid (500 mL) in a 3 L 3-necked flask fitted with a mechanical stirrer, a dropping funnel and a thermometer. The solution was cooled to 10-12° C. with an ice bath and sodium cyanoborohydride (64 g, 1.0 mol) was added in portions while ensuring the temperature remained at or below 15-16° C. After the addition was complete the cooling bath was removed and the reaction was warmed to ambient temperature for 0.5 hour. TLC (1:1 EtOAc/hexane) confirmed a complete reaction. The reaction was cooled to 5-10° C. and 50% aqueous sodium hydroxide was added until the pH was 8-10. The product oiled out and was extracted with ethyl acetate (3×700 mL). The combined organic layers were washed with water (2×500 mL) and brine (400 mL), dried over anhydrous potassium carbonate, filtered and concentrated to afford 5-methoxyindoline (50 g, 0.337 mol, 99% yield) as a thick oil. This product was used without further purification. The structure was corroborated by NMR spectroscopy.

Step 1L. Synthesis of 5-methylindoline

5-Methylindoline was prepared from 5-methylindole using the procedure described for the preparation of 5-methoxyindoline. 5-Methylindole (11 g, 0.0835 mol) in glacial acetic acid (150 mL) in a 1 L 3-necked flask was reduced at 10-15° C. with sodium cyanoborohydride (15.8 g, 0.251 mol). Extraction with ethyl acetate provided 5-methylindoline (11 g, 0.0832 mol, 99% yield) as a thick oil which was used without further purification. The structure was corroborated by NMR spectroscopy.

Step 1M. Synthesis of 3′,6′,4,5,6,7-hexachlorofluoran

Acetonitrile (680 mL), dimethylformamide (7 mL), tetrachlorofluorescein (170 g, 0.36 mol) and thionyl chloride (215 g, 1.8 mol) were added to a 3-liter 3-neck round bottom flask fitted with a mechanical stirrer, condenser and nitrogen inlet tube. Upon heating, a solution was briefly obtained followed by gradual crystallization of the product. The mixture was further heated at reflux (72° C.) for six hours. After cooling to room temperature, water (100 mL) was slowly and carefully added. The product was filtered and washed well with acetonitrile. Air drying provided a pale violet solid (141.5 g, 0.279 mol, 77% yield). The crude product was stirred in dimethylformamide (425 mL), heated to 100° C., and allowed to stand overnight. The pale violet crystals were filtered, washed with dimethylformamide followed by methanol and dried under vacuum at 60° C. to provide hexachlorofluoran (98.7 g, 0.195 mol, 54% yield). Assay by HPLC was 97% by area.

Step 1N. Synthesis of 3′-indolino-6′,4,5,6,7-pentachlorofluoran

Hexachlorofluoran (5.07 g, 10 mmol), 2,6-lutidine (1.07 g, 10 mmol), aluminum chloride (9.33 g, 70 mmol) and sulfolane (50 mL) were added to a 100 mL 3-neck round bottom flask fitted with a mechanical stirrer, condenser, thermometer and nitrogen inlet tube. The mixture was heated to 100° C. and indoline (1.19 g, lOmmol) was added. The temperature was raised to 180° C. and heating continued for 6 hours. After cooling to room temperature, the mixture was poured into cold water (250 mL) with rapid agitation. The blue-gray solid was filtered, washed with water and air-dried providing the crude product (5 g). The crude product was stirred in dimethylformamide (20 mL), heated to 100° C. and allowed to stand overnight. The resulting pale green solid was filtered, washed first with dimethylformamide followed by methanol and dried under vacuum at 60° C. to provide 3-indolinopentachlorofluoran (3.60 g, 6.1 mmol, 61% yeld). Assay by HPLC was 97% by area.

Step 1P. Synthesis of 3′-(5-methoxyindolino)-6′,4,5,6,7-pentachlorofluoran

Hexachlorofluoran (20 g, 0.0394 mol), aluminum chloride (20.8 g, 0.156 mol) and sulfolane (100 g) were added to a 250 mL 3-neck round bottom flask fitted with a mechanical stirrer, condenser, thermometer and nitrogen inlet tube. The mixture was heated to 120° C. and 5-methoxyindoline (12 g, 0.081 mol) was added. The reaction mixture was heated overnight at 120° C. After cooling to room temperature, the mixture was poured into cold water (1 L) with rapid agitation. The solid was filtered, washed with water and air-dried for several days followed by vacuum drying at 70° C. to give the crude product (25.5 g, 0.041 mol, 104% yield) which was used without further purification.

Step 1Q. Synthesis of 4,5,6,7-tetrafluorofluorescein

Using a mechanical stirrer, tetrafluorophthalic anhydride (50 g, 0.227 mol) was dissolved in methanesulfonic acid (221 mL). The anhydride dissolved completely as the temperature reached 40° C. When the temperature had reached 120° C., resorcinol (62.3 g, 0.568 mol) was added in 3 portions giving enough time between additions for the material to go into solution. The solution turned pale red. An HPLC of the reaction mixture was taken at the start of the reaction and every hour thereafter. The reaction was complete after three hours. Heating was stopped and the reaction mixture was allowed to cool to ambient temperature. The dark semi-solid residue was slowly poured into rapidly stirred ice water (2 L). A fine, olive-green solid precipitated in the water. The solid suspension was extracted with ethyl acetate (1 L) followed by further extractions with ethyl acetate (4×400 mL). The organic fractions were combined and dried over anhydrous magnesium sulfate (250 g). After stirring overnight, the drying agent was removed by vacuum filtration through a Celite pad. The ethyl acetate was removed on a rotary evaporator to give a dark brown-black solid (95 g) that was not further purified. The solid was dried in a vacuum desiccator overnight at 70° C.

Step 1R. Synthesis of 3′,6′-Dichloro-4,5,6,7-tetrafluoran

Using a mechanical stirrer, tetrafluorofluorescein (95 g, ca. 0.235 mol) was suspended in a mixture of acetonitrile (350 mL) and dimethylformamide (5.8 mL). Thionyl chloride (79 mL, 129.3 g, 1.08 mol) was added to this mixture. The reaction mixture was heated to reflux for 4 hours. HPLC showed complete conversion after 4 hours. The excess acetonitrile and excess thionyl chloride were removed by distillation in a stream of nitrogen. When nearly all of the solvent had been removed, the solid was resuspended in a solution of acetonitrile/water (95:5). The violet-brown solid was collected by vacuum filtration, washed with 95:5 acetonitrile/water (500 mL) followed by drying in a vacuum desiccator at 70° C. for 4 hours to give the desired product (84 g, 0.19 mol, 80% yield).

Step 1S. Synthesis of 3′-indolino-6′chloro-4,5,6,7-tetrafluorofluoran

3′,6′-Dichloro-4,5,6,7-tetrafluorofloran (20 g, 0.045 mol), 2,6-lutidine (4.74 g, 0.045 mol) and sulfolane (56 mL) were added to a 250 mL 3-neck round bottom flask fitted with a mechanical stirrer. Aluminum chloride (40.2 g, 0.28 mol) was added in small portions and the resulting mixture was stirred for 20 minutes. The temperature rose to 110° C. Indoline (5.13 g, 0.045 mol) was added slowly followed by 2,6-lutidine (4.74 g, 0.045 mol) and the reaction was heated at 110° C. for 5 hours. The reaction was followed to completion by HPLC. The reaction was poured into a mixture of crushed ice and water with vigorous agitation. The dark blue solid was collected by suction filtration, washed with water and dried under vacuum. The crude product was passed through a silica gel plug (300 g) using methylene chloride to elute. Removal of solvent provided the indolinofluoran as a yellow-green foam (16 g, 0.031 mol, 68% yield). The structure was confirmed by NMR and mass spectroscopy.

Step 1T. Synthesis of 3′-(5-methylindolino)-6′chloro-4,5,6,7-tetrafluorofluoran

3′,6′-Dichloro-4,5,6,7-tetrafluorofluoran (13.23 g, 0.030 mol), 2,6-lutidine (6.43 g, 0.060 mol) and sulfolane (30M1) were added to a 100 mL 3-neck round bottom flask fitted with a condenser. Aluminum chloride (16 g, 0.120 mol) was added followed by 5-methylindoline (4.0 g, 0.030 mol) and the reaction was heated at 110-120° C. for 20 hours under nitrogen. The reaction mixture was poured into a mixture of crushed ice, water, and hydrochloric acid (500 mL) with vigorous agitation and stirred for 0.5 hour. The solid was dissolved in ethyl acetate and washed with 10% sodium bicarbonate solution. The organic layer was separated, dried over sodium sulfate and concentrated The crude product was passed through a short column of silica gel using methylene chloride to elute. Removal of solvent provided the 3′-(5-methylindolino)-6′-chloro-4,5,6,7-tetraflourofluoran as a solid (4.6 g, 8.5 mmol, 28% yield).

The structure was confirmed by NMR and mass spectroscopy.

Example II

Synthesis of Dye I

A mixture of hexachlorofluoran (2.0 g, 3.9 mmol), 2,3,3-trimethylindoline (0.9 g; 5.9 mmol), zinc chloride (1.6 g; 11.8 mmol), and zinc oxide (0.5 g; 5.9 mol) in sulfolane (6 g) was stirred with heating at 190° C. for 4 hours. To this mixture was added aniline (0.8 g; 7.9 mmol) and the mixture was then further stirred with heating at 160° C. for 14 hours. The mixture was cooled to 50° C. and quenched into 2N HCl (100 mL). The crude solid was isolated by filtration, washed with water several times and taken up in methylene chloride (150 mL). The methylene chloride solution was washed with sat. sodium bicarbonate (2×100 mL), dried over magnesium sulfate and the solvent removed. The residual solid was purified by column chromatography on silica gel (eluted with 30% ethyl acetate in hexane) to give 0.6 g pure product (22% yield) and then recrystallized from ca. 10% acetone in hexane to give colorless crystalline product, m.p. 210-215° C. (0.35 g, 13% yield). The structure was confirmed by proton NMR and mass spectroscopy.

Example III

Synthesis of Dye II

A mixture of hexachlorofluoran (2.0 g, 3.9 mmol), indoline (0.7 g, 5.9 mmol), zinc chloride (1.6 g, 11.8 mmol), and zinc oxide (0.5 g, 5.9 mmol) in sulfolane (6 g) was stirred with heating at 145° C. for 90 minutes. To this mixture was added 4-(2-ethyl-1-hexyloxy) aniline (2.7 g, 7.9 mmol) and the mixture was further stirred with heating at 160° C. for 5 hours. The mixture was cooled to 50° C. and quenched into 2N HCl (100 mL). The crude solid was isolated by filtration, washed with water several times and taken up in methylene chloride (150 mL). The methylene chloride solution was washed with sat. sodium bicarbonate (2×100 mL), dried over magnesium sulfate and the solvent was evaporated. The residual solid was purified by column chromatography (10% ethyl acetate in methylene chloride) to give 1.2 g pure product (39% yield) and recrystallized from approximately 10% acetone/hexane to give colorless crystalline product (0.55 g, m.p. 180-182° C., 18% yield). The structure was confirmed by proton NMR and mass spectroscopy.

Example IV

Synthesis of Dye III

Pentachloroindolinofluoran (11.8 g, 20 mmol), ZnCl₂ (8.2 g, 60 mmol) and ZnO (2.43 g, 30 mmol) were added to a 250 ml round bottom flask containing sulfolane (30 g) and the flask warmed to dissolve the solids. To the hot blue solution was added 3,4-dioctyloxyaniline (13.96 g, 40 mmol) and the flask was placed with an air condenser into an oil bath preheated to 140° C. The reaction mixture was stirred at that temperature for 2 hours. The reaction was followed by TLC (25% ethyl acetate in hexane) until complete. The reaction mixture was cooled and 2N HCl (400 mL) was added followed by trituration with a spatula to break the large blue mass to a crystalline powder. The reaction mixture was filtered and washed copiously with water. The crude product was dissolved in ethyl acetate (1200 mL) and extracted with 10% Na₂CO₃ (2×250 mL), followed by water and brine (250 mL each). The organic layer was dried over sodium sulfate and evaporated to yield crude blue product (23 g). The crude product was purified on a silica gel column (1.5Kg) packed in methylene chloride. The product was eluted with 10% ethyl acetate/methylene chloride (5 L). Pure fractions were pooled to obtain the product as a glass (13.5 g) which was crystallized from 10% acetone in hexane to obtain a first crop of colorless crystals (8.5 g, 9.4 mmol, 47% yield). Recrystallization of the mother liquor provided a second crop of crystals (2.5 g, 2.7 mmol, 13.5% yield). The overall yield was 11.0 g, 12.1 mmol, 60.5% yield. NMR analysis and mass spectroscopy confirmed the structure.

Example V

Synthesis of Dye IV

3′-Indolinopentachlorofluorescin (2.15 g, 3.6 mmol), 4-(2-hydroxy-1-decyloxy)aniline (1,81 g, 6.8 mmol), zinc chloride (1.5 g, 11 mmol), zinc oxide (0.45 g, 5.6 mmol) and tetramethylene sulfone (8 g) were added to a 100-mL flask. The reaction mixture was heated at 150° C. for 12 hours under an atmosphere of nitrogen. The cooled mixture was poured into 2N hydrochloric acid (100 mL). A dark blue precipitate was obtained and filtered and washed with 0.5N aq. hydrochloric acid solution (100 mL) and water (100 mL). The crude product was purified by silica gel column chromatography (loaded and eluted with 500 ml of methylene chloride, followed by 500 ml of 1% methanol/methylene chloride). The solvent was removed by rotary evaporation to collect a dark blue powder (2.3 g, 2.77 mmol, 77% yield). Pale greenish crystals were obtained by recrystallization from 10% acetone/hexanes. m.p: 156-158° C. The structure was confirmed by proton NMR and mass spectroscopy.

Example VI

Synthesis of Dye V

A mixture of hexachlorofluoran (1.0 g, 1.9 mmol), 5-methoxyindoline (0.5 g, 3.0 mmol), zinc chloride (0.8 g, 5.9 mmol), and zinc oxide (0.3 g, 2.5 mmol) in sulfolane (4 g) was stirred with heating at 145° C. for 2 hours. To this mixture was added 3, 4-dioctyloxyaniline (1.4 g, 4.0 mmol) and the mixture was further stirred with heating at 160° C. for 5 hours. The mixture was cooled to 50° C. and quenched into 2N HCl (100 mL). The crude solid was isolated by filtration, washed with water several times and taken up in methylene chloride (150 mL). The methylene chloride solution was washed with sat. sodium bicarbonate (2 x 100 mL), dried over magnesium sulfate and the solvent was removed. The residual solid was purified by column chromatography on silica gel eluted with 20% ethyl acetate in methylene chloride to give pure product (0.80 g, 0.836 mmol, 44% yield) which was recrystallized from acetonitrile to give colorless crystalline product (0.35 g, 0.836 mmol, 19% yield) m.p. 117-119° C. The structure was confirmed by proton NMR and mass spectroscopy.

Example VII

Synthesis of Dye VI

A mixture of 3′-indolino-6′-chloro-4,5,6,7-tetrafluorofloran (1.0 g, 1.9 mmol), zinc chloride (0.8 g, 5.7 mmol), zinc oxide (0.2 g, 2.8 mmol), and 2-isopropylanilne (0.5 g, 3.8 mmol) in sulfolane (4 g) was stirred with heating at 160° C. for 14 hours. The mixture was cooled to 50° C. and quenched into 2N HCl (100 mL). The crude solid was isolated by filtration, washed with water several times and taken up in methylene chloride (150 mL). This methylene chloride solution was washed with sat. sodium bicarbonate (2 x 100 mL), and dried over magnesium sulfate to remove the solvent. The residual solid was purified by column chromatography on silica gel eluted with 35% ethyl acetate in methylene chloride to give pure product (0.60 g, 0.95 mmol, 50% yield) which was recrystallized from 10% acetone in hexane to give colorless crystalline product (0.3 g, 0.475 mmol, 25% yield) m.p. 209-210° C. The structure was confirmed by proton NMR and mass spectroscopy.

Example VIII

Synthesis of Dye VII

A mixture of 3′-indolino-6′-chloro-4,5,6,7-tetrafluorofluoran (7.80 g, 15 mmol), zinc chloride (6.13 g, 45 mmol), zinc oxide (1.22 g, 15 mmol), and 2-methyl-4-decyloxyaniline (7.89 g, 30 mmol) in sulfolane (30 g) was stirred with heating at 160-170° C. for 24 hours. Analysis by TLC (30% ethyl acetate/methylene chloride) showed a major product at Rf=0.5 with a mass spectrum consistent with the product (M+1=751). The reaction mixture was poured onto a mixture of ice/water/hydrochloric acid, stirred for ½ hour, filtered and dried. The crude product was dissolved in ethyl acetate (700 mL) and stirred for one hour with 10% sodium bicarbonate solution (300 mL). After filtration through a pad of Celite the organic layer was separated, dried over sodium sulfate and concentrated to a thick oil. Column chromatography on silica gel (400 g, 10-30% ethyl acetate/methylene chloride) provided pure fractions which were concentrated and recrystallized from acetone/hexane to yield colorless crystals (5.85 g), m.p. 137-139° C. A second crop (1.0 g) was obtained to give a total of 6.85 g (9.12 mmol, 61% yield). The structure was confirmed by NMR and mass spectroscopy.

Example IX

Synthesis of Dye VIII

A mixture of 3′-(5-methylindolino)-6′-chloro-4,5,6,7-tetrafluorofluoran (1.343 g, 2.5 mmol), zinc chloride (1.022 g, 7.5 mmol), zinc oxide (0.203 g, 2.5 mmol), and 2-methyl-4-decyloxyaniline (1.375 g, 5 mmol) in sulfolane (5 g) was stirred with heating at 160-175° C. for 24 hours. The reaction mixture was poured onto a mixture of ice/water/hydrochloric acid, stirred for ½ hour, filtered and dried. The crude product was dissolved in methylene chloride, treated with triethylamine (7 mL) and evaporated. Column chromatography on silica gel (250 mL, 50% ethyl acetate/methylene chloride) provided pure fractions which were concentrated and recrystallized from acetone/hexane to yield colorless crystals (0.700 g, 0.915 mmol, 37% yield) m.p. 170-171.5° C. The structure was confirmed by NMR and mass spectroscopy.

Example X

Synthesis of Dye IX

A mixture of 3′-indolino-6′-chloro-4,5,6,7-tetrafluorofluoran (1.0 g, 1.9 mmol), zinc chloride (0.8 g, 5.7 mmol), zinc oxide (0.2 g, 2.8 mmol), and 2-methyl-4-octadecyloxyanilne (1.4 g, 3.8 mmol) in sulfolane (4 g) was stirred with heating at 160° C. for 14 hours. The mixture was cooled to 50° C. and quenched into 2N HCl (100 mL). The crude solid was isolated by filtration, washed with water several times and taken up in methylene chloride (150 mL). This methylene chloride solution was washed with sat. sodium bicarbonate (2×100 mL) and dried over magnesium sulfate to remove the the solvent. The residual solid was purified by column chromatography on silica gel eluted with 35% ethyl acetate in methylene chloride to give pure product (1.0 g, 116 mmol, 61% yield) which was recrystallized from 10% acetone in hexane to give colorless crystalline product (0.5 g, 0.57 mmol, 30% yield); m.p. 136-138° C.). The structure was confirmed by NMR and mass spectroscopy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, side sectional view of a three-color thermal imaging member according to the invention.

SUMMARY OF THE INVENTION

It is an object of this invention to provide novel thermal imaging members and methods.

Another object of the invention is to provide thermal imaging members and methods that utilize a color-former that exhibits different colors when in a crystalline form than when in an amorphous form.

Yet another object of the invention is to provide imaging members and methods that utilize certain rhodamine color-formers.

According to one aspect of the invention there are provided novel thermal imaging members and methods that utilize certain rhodamine color-forming compounds that exhibit a first color when in a crystalline form and a second color, different from the first color, when in an amorphous form.

In one embodiment of the invention there are provided novel thermal imaging members and methods that utilize compounds that are represented by formula I:

wherein:

R₁, R₃, R₄, R₅, R₆ and R₇ are each independently selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted, alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, halogen, nitro, nitrilo, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, oxygen, substituted oxygen, nitrogen, substituted nitrogen, sulfur and substituted sulfur;

R₂ is selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, substituted oxygen, substituted nitrogen and substituted sulfur;

R₈ is absent or selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, halogen, nitro, nitrilo, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, oxygen, substituted oxygen, nitrogen, substituted nitrogen, sulfur and substituted sulfur;

R₉, R₁₀ and R₁₁ are independently selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, halogen, nitro, nitrilo, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, oxygen, substituted oxygen, nitrogen, substituted nitrogen, sulfur and substituted sulfur;

R₁₂, R₁₃, R₁₄ and R₁₅ are independently selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, aryl, substituted aryl, heteroaryl, and substituted heteroaryl;

R₁₆, R₁₇, R₁₈ and R₁₉ are independently selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, halogen, nitro, nitrilo, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, oxygen, substituted oxygen, nitrogen, substituted nitrogen, sulfur and substituted sulfur; and

X₁ is carbon or nitrogen; wherein the compound of formula I is in the crystalline form.

Preferred thermal imaging members and methods of the present invention comprise a compound represented by formula I in which R₈, R₉, R₁₀ and R₁₁ are fluorine, R₁₂ and R₁₃ are hydrogen atoms, R₁₄ and R₁₅ are identical alkyl groups, preferably methyl groups, R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₁₆, R₁₇, R₁₈ and R₁₉ are as previously defined and X₁ is carbon.

In another aspect of the present invention there are provided compounds of formula I in which:

R₁, R₃, R₄, R₅, R₆ and R₇ are each independently selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted, alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, halogen, nitro, nitrilo, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, oxygen, substituted oxygen, nitrogen, substituted nitrogen, sulfur and substituted sulfur;

R₂ is selected from the group consisting of aryl and substituted aryl;

R₈, R₉, R₁₀ and R₁₁ are fluorine; R₁₂ and R₁₃ are hydrogen atoms;

R₁₄ and R₁₅ are identical substituents selected from the group consisting of alkyl having from 1 to 18 carbon atoms and substituted alkyl having from 1 to 18 carbon atoms;

R₁₆, R₁₇, R₁₈ and R₁₉ are independently selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, halogen, nitro, nitrilo, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, oxygen, substituted oxygen, nitrogen, substituted nitrogen, sulfur and substituted sulfur; and

X₁ is carbon.

In yet another aspect of the present invention there is provided a compound of formula I in which R₂ is a 2,4-dimethylphenyl group, R₈, R₉, R₁₀ and R₁₁ are fluorine, R₁₄, R₁₅ and R₁₇ are methyl groups, R₁, R₃, R₄, R₅, R₆, R₇, R₁₂, R₁₃, R₁₆, R₁₈ and R₁₉ are hydrogen and X₁is carbon, i.e., 3′-(3,3,5-trimethylindolino)-6′-(2,4-dimethylanilino)-4,5,6,7-tetrafluorofluoran.

DETAILED DESCRIPTION

According to the present invention, the compounds of formula I may be incorporated into any thermal imaging members and used in any thermal imaging methods, including direct thermal imaging members and thermal transfer imaging members and methods.

Preferred thermal imaging members according to the invention are direct thermal imaging members, particularly those having the structures described in U.S. Pat. No. 6,801,233 B2 and U.S. patent application Ser. No. 11/400735, filed Apr. 6, 2006.

Other preferred thermal imaging members are those for use in thermal transfer imaging methods, particularly those having the structures described in U.S. Pat. No. 6,537,410.

Further preferred thermal imaging members are thermal transfer imaging members having the structures described in commonly assigned U.S. Pat. No. 6,054,246.

Direct thermal imaging members according to the invention, for use in direct thermal printing methods, include all the color-forming reagents necessary to form an image in the member itself. Direct thermal imaging members according to the invention generally comprise a substrate carrying at least one image-forming layer that includes a compound according to formula I in the crystalline form. The crystalline form of a compound of formula I can be converted at least partially to an amorphous form, the amorphous form having intrinsically a different color from the crystalline form. The imaging member may be monochromatic, in which an image-forming layer includes at least one compound of formula I, or polychromatic. Multicolor direct thermal imaging members include at least two, and preferably three, image-forming layers, and the temperature at which an image is formed in at least one of the image-forming layers is preferably time-interval-independent. Preferred imaging members according to the invention are direct multicolor thermal imaging members.

The conversion from the crystalline form to the amorphous form in accordance with the thermal imaging members and thermal imaging methods of the invention is carried out by applying heat to compositions comprising the compounds of formula I. In the thermal imaging methods of the invention, heat may be applied to the thermal imaging members that contain compositions comprising the compounds of formula I by any of the techniques known in thermal imaging such as from a thermal print head, a laser, a heated stylus, etc.

In one embodiment of the present invention, one or more thermal solvents, which are crystalline materials, can be incorporated in the thermal imaging member. The crystalline thermal solvent(s), upon being heated, melt and thereafter dissolve or liquefy the crystalline color-forming material of formula I, thereby converting it to the amorphous form and providing a color change (i.e., an image). Thermal solvents may be advantageously used when it is required for a color-forming layer in a direct thermal imaging member to have an activation temperature (the temperature at which color is formed or at which color changes) that is lower than the melting point of the compound of formula I. The melting point of the thermal solvent, rather than that of the compound of formula I, may in such a case establish the activation temperature of a color-forming layer.

It will be clear to one of ordinary skill in the art that the activation temperature of a color-forming layer that comprises a mixture of crystalline materials may be different from the melting points of any of the individual components. A eutectic mixture of two crystalline components, for example, melts at a lower temperature than either of the components in isolation. Conversely, if the rate of solubilization of the compound of formula I in the molten thermal solvent is slow, the activation temperature of the mixture may be higher than the melting point of the thermal solvent. Recall that the activation temperature of a mixture of a compound of formula I and a thermal solvent is the temperature at which the color of the mixture changes, i.e., the temperature at which a sufficient amount of the compound of formula I dissolves in the molten thermal solvent to provide a visible color change. It will be clear from the above discussion that the activation temperatures of mixtures of compounds of formula I and thermal solvents may be dependent upon the rate of heating. For these reasons, in the design of thermal imaging members of the present invention determination of the actual activation temperature of a composition is preferred to be carried out experimentally.

Any suitable thermal solvents may be incorporated in the thermal imaging members of the invention. Suitable thermal solvents include, for example, aromatic and aliphatic ethers, diethers and polyethers, alkanols containing at least about 12 carbon atoms, alkanediols containing at least about 12 carbon atoms, monocarboxylic acids containing at least about 12 carbon atoms, esters and amides of such acids, aryl amides, especially benzanilides, aryl sulfonamides and hydroxyalkyl-substituted arenes.

Specific preferred thermal solvents include: 1,2-diphenoxyethane, 1,2-bis(4-methylphenoxy)ethane, tetradecan-1-ol, hexadecan-1-ol, octadecan-1-ol, dodecane-1,2-diol, hexadecane-1,16-diol, myristic acid, palmitic acid, stearic acid, methyl docosanoate, 1,4-bis(hydroxymethyl)benzene, and p-toluenesulfonamide.

Particularly preferred thermal solvents are diaryl sulfones such as diphenylsulfone, 4,4′-dimethyldiphenylsulfone, phenyl p-tolylsulfone and 4, 4′-dichlorodiphenylsulfone, and ethers such as 1,2-bis(2,4-dimethylphenoxy)ethane, 1,4-bis(4-methylphenoxymethyl)benzene and 1,4-bis(benzyloxy)benzene.

When converted to the colored form the compounds of formula I (in the closed form) have the open form illustrated by formula II:

wherein R₁-R₁₉ and X₁ are as defined above with respect to formula I.

It is possible that the dissolution of the compounds of formula I by a thermal solvent may lead to an amorphous form (in which the compound is dissolved in the amorphous thermal solvent) in which the proportion of the open, colored form is different from the proportion that would be present in the amorphous form resulting from melting the compound of formula I alone (i.e., without interaction with the thermal solvent). In particular, the proportion of the open, colored form of the compound in the amorphous material may be enhanced by use of hydrogen-bonding or acidic thermal solvents. Materials that increase the proportion of the color-forming material that is in the open, colored form are hereinafter referred to as “developers”. It is possible that the same compound may serve the function of thermal solvent and developer. Preferred developers include phenols such as 2,2′-methylenebis(6-tert-butyl-4-methylphenol), 2,2′-methylenebis(6-tert-butyl-4-ethylphenol), 2,2′-ethylidenebis(4,6-di-tert-butylphenol), bis[2-hydroxy-5-methyl-3-(1-methylcyclohexyl)phenyl]methane, 1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl)isocyanurate, 2,6-bis[[3-(1,1-dimethylethyl)-2-hydroxy-5-methylphenyl]methyl]-4-methylphenol, 2,2′-butylidenebis[6-(1,1-dimethylethyl)-4-methylphenol, 2,2′-(3,5,5-trimethylhexylidene)bis[4,6-dimethyl-phenol], 2,2′-methylenebis[4,6-bis(1,1-dimethylethyl)-phenol, 2,2′-(2-methylpropylidene)bis[4,6-dimethyl-phenol], 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, 2,2′-thiobis(4-tert-octylphenol), and 3-tert-butyl-4-hydroxy-5-methylphenyl sulfide.

In order for the image formed by the amorphous color-former to be stable against recrystallization back to the crystalline form, preferably the glass transition temperature (T_(g)) of the amorphous mixture of the color-former and any thermal solvent should be higher than any temperature that the final image must survive. Typically, it is preferred that the T_(g) of the amorphous, colored material be at least about 50° C., and ideally above about 60° C. In order to ensure that the T_(g) is sufficiently high for a stable image to be formed, materials having a high T_(g) may be added to the color-forming composition. Such materials, hereinafter referred to as “stabilizers”, when dissolved in the amorphous mixture of color-former, optional thermal solvent, and optional developer, serve to increase the thermal stability of the image.

Preferred stabilizers have a T_(g) that is at least about 60° C., and preferably above about 80° C. Examples of such stabilizers are the aforementioned 1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl)isocyanurate (T_(g) 123° C.) and 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane (T_(g) 101° C.). The stabilizer molecule may also serve as a thermal solvent or as a developer.

For example, the color-forming material may itself have a melting temperature above the desired temperature for imaging, and a T_(g) (in the amorphous form) of about 60° C. In order to produce a color-forming composition melting a the desired temperature, it may be combined with a thermal solvent (for example, a diaryl sulfone) that melts at the desired temperature for imaging. The combination of thermal solvent and color-forming material may, however, have a T_(g) that is substantially lower than 60° C., rendering the (amorphous) image unstable. In this case, a stabilizer such as 1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl)isocyanurate may be added, to raise the T_(g) of the amorphous material. In addition, there may be provided a developer, for example, a phenolic compound such as 2,2′-ethylidenebis(4,6-di-tert-butylphenol), in order to increase the proportion of the color-forming material that is in the colored form in the amorphous phase.

Preferably the color-forming compound of the present invention, the (optional) thermal solvent, the (optional) developer and the (optional) stabilizer are each predominantly in their crystalline forms prior to imaging. By “predominantly” is meant at least about 50%). During imaging, at least one of these materials melts and an amorphous mixture of the materials is formed. The amorphous mixture is colored, whereas the crystalline starting materials are not.

It is possible that one of the components in the amorphous, colored mixture may recrystallize after the image has been formed. It is desirable that such recrystallization not change the color of the image. In the case that a color-former, thermal solvent, developer and stabilizer are used, the thermal solvent may typically recrystallize without greatly affecting the color of the image.

The substituents on the compounds of formula I are preferably chosen to minimize the water solubility of the compounds and facilitate the formation of a colorless form in non-polar, non-protic solvents. This is because the manufacture of a thermal imaging member of the present invention typically involves an aqueous coating process. Were the compound of formula I to dissolve appreciably in water (the coating solvent), the coloration that is intended to occur when heating the thermal imaging member itself would occur prematurely during manufacture. On the other hand, the thermal solvents, when used, are typically non-polar, non-protic solvents, and are intended to dissolve the compounds of formula I.

Another consideration that influences the choice of substituents on the compounds of formula I is the color provided by the open form, namely formula II. Compounds of formula II (in the open form) typically exhibit maximum absorption of light in the range of 600-700 nm. As such, these compounds are typically cyan dyes. As discussed above, the quality of the cyan chromophore is typically optimized when substituents R₈-R₁₁ are electron-withdrawing relative to hydrogen, and X₁ is carbon. In dyes I-V described above, substituents R₈-R₁₁ are chlorine atoms, while in dyes VI-IX substituents R₈-R₁₁ are fluorine atoms.

Yet another consideration is the stability of the image formed by the compound of formula I. When used in a direct thermal imaging member, the colorless form of the compound (formula I itself) and the colored form of the compound (formula II) each must be stable, since in such imaging members the material is present both in colored and uncolored regions. In particular, the forms represented by formulas I and II must be stable to ultraviolet light and to oxidation in the presence or absence of light of any wavelength. The present inventors have found that the colored form (formula II) of dyes such as dyes I-V, in which substituents R₈-R₁₁ are chlorine atoms, may be prone to darkening to an almost black color in the presence of light and oxygen, whereas the colored form of dyes such as VI-IX, in which substituents R₈-R₁₁ are fluorine atoms, is much more stable under these conditions.

As used in thermal imaging members of the present invention, the colorless form of compounds is, as noted above, present in the crystalline state. The stability of the colorless form in the crystalline state may be compromised if any reactions, particularly photochemical reactions, occur within or at the surface of crystals of the compounds. As noted above, it is preferred (for optimization of the chromophore) that substituents R₈-R₁₁ be electron-withdrawing relative to hydrogen, preferably halogen substituents. The resulting highly substituted phenyl substituent then becomes, however, an excellent electron acceptor that can participate in electron transfer reactions with electron donating groups. Such reactions can be facilitated by the absorption of light, particularly light of short wavelengths.

Those of ordinary skill in the art will notice that the compounds of formula I, in the non-colored form, comprise electron-donating portions (the indoline and amino substituents) and, as noted, electron-accepting portions (the lower benzene ring when substituted with four halogen atoms). The present inventors have found that certain compounds of formula I can self-oxidize in the crystalline form, in the presence of light of ultraviolet and short blue wavelengths. This reaction causes the colorless crystals of such compounds to darken. When the darkened crystals are analyzed, it is found that a common product involves oxidation of the indoline portion of the molecule to an indole.

This reaction, being an oxidation, involves loss of a hydrogen atom from one of positions R₁₂ and R₁₃ and one of positions R₁₄ and R₁₅. Therefore, its occurrence can be prevented if neither of R₁₂ and R₁₃ is a hydrogen atom, and/or neither R₁₄ and R₁₅ of is a hydrogen atom. The synthesis of compounds of formula I in which substituents R₁₄ and R₁₅ are other than hydrogen is more straightforward than the alternative in which substituents R₁₂ and R₁₃ are other than hydrogen, as will be clear to one of ordinary skill in the art. The present inventors have found that undesirable coloration of the colorless, crystalline form of compounds of the present invention in the presence of light is greatly reduced when substituents R₁₄ and R₁₅ are both alkyl groups, preferably methyl groups.

In compound I, above, the three groups R₁₃, R₁₄ and R₁₅ are methyl groups. However, as will be clear to one of ordinary skill in the art, in this case there become two chiral centers in the compound: that at the carbon atom that bears the R₁₃ substituent, and that at the spiro center of the lactone ring. The presence of two chiral centers means that the compound can exist as two diastereoisomers, which having different shapes from each other may not pack easily into a crystalline form. It is preferred, for ease of crystallization, that diastereoisomeric mixtures not be used in the practice of the present invention.

For this reason, it is preferred that substituents R₁₂ and R₁₃ both be hydrogen atoms, and substituents R₁₄ and R₁₅ both be identical alkyl groups, preferably methyl groups.

A particularly preferred compound of formula I in which substituents R₈-R₁₁ are fluorine atoms, substituents R₁₂ and R₁₃ are both hydrogen atoms, and substituents R₁₄ and R₁₅ are both methyl groups is dye X, 3′-(3,3,5-trimethylindolino)-6′-(2,4-dimethylanilino)-4,5,6,7-tetrafluorofluoran.

The compounds used according to the invention may be prepared by synthetic processes which are known to those skilled in the art, particularly in view of the state of the art in organic synthetic processes, and the present disclosure and specific preparatory examples provided below herein.

Generally, symmetrical rhodamine dyes can be prepared in one step from 3′,6′-dichlorofluorans by reacting two equivalents of an aromatic or aliphatic amine as described in U.S. Pat. 4,602,263, GB2311075 and DE81056. The unsymmetrical rhodamine dyes are then prepared by the selective monoalkylation of symmetrical rhodamines using sodium hydride in dimethyl sulfoxide as described in U.S. Pat. Nos. 4,602,263 and 4,826,976.

Alternatively, the unsymmetrical rhodamines can be prepared by use of an alternate synthetic pathway in which one equivalent of an N-alkylaniline is reacted selectively with the 3′,6′-dichlorofluoran using aluminum chloride as a catalyst to produce 3′-chloro-6′-N-alkyl-N-arylfluorans. These products are isolated and purified prior to reacting with a second equivalent of an aromatic or aliphatic amine. Zinc chloride is used as the catalyst for the second addition. DE139727 describes the selective addition of anilines to 3′,6′-dichlorofluorans to produce 3′-chloro-6′-arylaminofluorans using a mixture of zinc chloride and zinc oxide at 160° C.

Unsymmetrical rhodamines can also be made from 2-benzoyl benzoic acid derivatives by condensation with 3-arylamino phenols or 3-alkylamino phenols as described in Chemistry and Applications of Leuco Dyes, pp. 180-191 R. Muthyala, Ed., Plenum Press, New York and London, 1997 and also U.S. Pat. Nos. 4,390,616 and 4,436,920.

The 3′,6′-dichlorofluorans are synthesized from the corresponding fluoresceins using thionyl chloride and dimethylformamide in a variation of the method of Hurd described in the Journal of the Amer. Chemical Soc. 59, 112 (1937).

Careful recrystallization from solvent mixtures such as hexanes/acetone or hexanes/ethyl acetate produces colorless crystalline material which is preferred for use in thermal imaging members.

An example of the preparation of a preferred compound of the present invention, dye X, is given below.

One preferred thermal imaging member according to the present invention is constructed as follows.

The substrate is a filled, white poly(ethylene terephthalate) base of thickness about 75 microns, Melinex 339, available from Dupont Teijin Films, Hopewell, Va.

A first layer deposited on the substrate is an optional oxygen barrier layer composed of a fully hydrolyzed poly(vinyl alcohol), for example, Celvol 325, available from Celanese, Dallas, Tex. (96.7% by weight), glyoxal (a crosslinker, 3% by weight) and Zonyl FSN (a coating aid, available from Dupont, Wilmington, Del., 0.3% by weight). This layer, when present, has a coverage of about 1.0 g/m².

Deposited either directly onto the substrate, or onto the optional oxygen barrier layer, is a cyan color-forming layer composed of a cyan color-former, dye X of the present invention, having melting point 210° C., (1 part by weight), diphenyl sulfone (a thermal solvent having melting point 125° C., coated as an aqueous dispersion of crystals having average particle size under 1 micron, 3.4 parts by weight), Lowinox WSP (a phenolic antioxidant, available from Great Lakes Chemical Co., West Lafayette, Ind., coated as an aqueous dispersion of crystals having average particle size under 1 micron, 0.75 parts by weight), Chinox 1790 (a second phenolic antioxidant, available from Chitec Chemical, Taiwan, coated as an aqueous dispersion of crystals having average particle size under 1 micron, 1 part by weight), poly(vinyl alcohol) (a binder, Celvol 205, available from Celanese, Dallas, Tex., 2.7 parts by weight), glyoxal (0.084 parts by weight) and Zonyl FSN (0.048 parts by weight). This layer has a coverage of about 2.5 g/m².

Deposited onto the cyan color-forming layer is a barrier layer that contains a fluorescent brightener. This layer is composed of a fully hydrolyzed poly(vinyl alcohol), for example, the abovementioned Celvol 325, available from Celanese, Dallas, Tex. (3.75 parts by weight), glyoxal (0.08 parts by weight), Leucophor BCF P115 (a fluorescent brightener, available from Clariant Corp., Charlotte, N.C., 0.5 parts by weight), boric acid (0.38 parts by weight) and Zonyl FSN (0.05 parts by weight). This layer has a coverage of about 1.5 g/m².

The fluorescent brightener serves the purpose in the present invention of absorbing short wavelength blue and ultraviolet light that might lead to instability of the crystalline form of the compound of the present invention that is present in the cyan color-forming layer. The absorbed light is re-emitted by fluorescence at a slightly longer wavelength, and thus the short blue absorbance does not lend a yellow color to the thermal imaging member. This would not be the case if a conventional absorber of short blue wavelengths were used.

Deposited on the barrier layer is a thermally-insulating interlayer composed of Glascol C-44 (a latex available from Ciba Specialty Chemicals Corporation, Tarrytown, N.Y., 18 parts by weight), Joncryl 1601 (a latex available from Johnson Polymer, Sturtevant, Wis., 12 parts by weight) and Zonyl FSN (0.02 parts by weight). This layer has a coverage of about 13 g/m².

Deposited on the thermally-insulating interlayer is a barrier layer composed of a fully hydrolyzed poly(vinyl alcohol), for example, the abovementioned Celvol 325, available from Celanese, Dallas, Tex. (2.47 parts by weight), glyoxal (0.07 parts by weight), boric acid (0.25 parts by weight) and Zonyl FSN (0.06 parts by weight). This layer has a coverage of about 1.0 g/m².

Deposited on the barrier layer is a magenta color-forming layer, composed of a magenta color-former, Dye IV described in U.S. patent application Ser. No. 11/433808, filed May 12, 2006, having a melting point of 152° C.; a phenolic antioxidant (Anox 29, having melting point 161-164° C., available from Great Lakes Chemical Co., West Lafayette, Ind., coated as an aqueous dispersion of crystals having average particle size under 1 micron, 3.58 parts by weight), Lowinox CA22 (a second phenolic antioxidant, available from Great Lakes Chemical Co., West Lafayette, Ind., coated as an aqueous dispersion of crystals having average particle size under 1 micron, 0.72 parts by weight), poly(vinyl alcohol) (a binder, Celvol 205, available from Celanese, Dallas, Tex., 2 parts by weight), the potassium salt of Carboset 325 (an acrylic copolymer, available from Noveon, Cleveland, Ohio, 1 part by weight) glyoxal (0.06 parts by weight) and Zonyl FSN (0.06 parts by weight). This layer has a coverage of about 2.7 g/m².

Deposited on the magenta color-forming layer is a barrier layer composed of a fully hydrolyzed poly(vinyl alcohol), for example, the abovementioned Celvol 325, available from Celanese, Dallas, Tex. (2.47 parts by weight), glyoxal (0.07 parts by weight), boric acid (0.25 parts by weight) and Zonyl FSN (0.06 parts by weight). This layer has a coverage of about 1.0 g/m².

Deposited on the barrier layer is a second thermally-insulating interlayer composed of Glascol C-44 (1 part by weight), Joncryl 1601 (a latex available from Johnson Polymer, 0.67 parts by weight) and Zonyl FSN (0.004 parts by weight). This layer has a coverage of about 2.5 g/m².

Deposited on the second interlayer is a barrier layer composed of a fully hydrolyzed poly(vinyl alcohol), for example, the abovementioned Celvol 325, available from Celanese, Dallas, Tex. (1 part by weight), glyoxal (0.03 parts by weight), boric acid (0.1 parts by weight) and Zonyl FSN (0.037 parts by weight). This layer has a coverage of about 0.5 g/m².

Deposited on the barrier layer is a yellow color-forming layer composed of Dye XI (having melting point 202-203° C.) described in U.S. Pat. No. 7,279,264 (4.57 parts by weight), poly(vinyl alcohol) (a binder, Celvol 540, available from Celanese, Dallas, Tex., 1.98 parts by weight), a colloidal silica (Snowtex 0-40, available from Nissan Chemical Industries, Ltd Tokoyo, Japan, 0.1 parts by weight), glyoxal (0.06 parts by weight) and Zonyl FSN (0.017 parts by weight). This layer has a coverage of about 1.6 g/m².

Deposited on the yellow color-forming layer is a barrier layer composed of a fully hydrolyzed poly(vinyl alcohol), for example, the abovementioned Celvol 325, available from Celanese, Dallas, Tex. (1 part by weight), glyoxal (0.03 parts by weight), boric acid (0.1 parts by weight) and Zonyl FSN (0.037 parts by weight). This layer has a coverage of about 0.5 g/m².

Deposited on the barrier layer is an ultra-violet blocking layer composed of a nanoparticulate grade of titanium dioxide (MS-7, available from Kobo Products Inc., South Plainfield, N.J., 1 part by weight), poly(vinyl alcohol) (a binder, Elvanol 40-16, available from DuPont, Wilmington, Del., 0.4 parts by weight), Curesan 199 (a crosslinker, available from BASF Corp., Appleton, Wis., 0.16 parts by weight) and Zonyl FSN (0.027 parts by weight). This layer has a coverage of about 1.56 g/m².

Deposited on the ultra-violet blocking layer is an overcoat composed of a latex (XK-101, available from NeoResins, Inc., Wilmingtom, Mass., 1 part by weight), a styrene/maleic acid copolymer (SMA 17352H, available from Sartomer Company, Wilmington, Pa., 0.17 parts by weight), a crosslinker (Bayhydur VPLS 2336, available from BayerMaterialScience, Pittsburgh, Pa., 1 part by weight), zinc stearate (Hidorin F-115P, available from Cytech Products Inc., Elizabethtown, Ky., 0.66 parts by weight) and Zonyl FSN (0.04 parts by weight). This layer has a coverage of about 0.75 g/m².

Representative conditions for printing a yellow image using this preferred thermal imaging member described above are as follows.

-   Thermal printing head parameters: -   Pixels per inch: 300 -   Resistor size: 2×(31.5×120) microns (split resistor) -   Resistance: 3000 Ohm -   Glaze Thickness: 110 microns -   Pressure: 3 lb/linear inch -   Dot pattern: Slanted grid.

The yellow color-forming layer is printed as shown in the table below. The line cycle time is divided into individual pulses of 75% duty cycle. The thermal imaging member is preheated by contact with the thermal printing head glaze at the heat sink temperature over a distance of about 0.3 mm.

Yellow printing Heat sink 25° C. temperature Dpi 300 (transport direction) Voltage 38 Line speed 6 inch/sec Pulse 12.5 microsec interval # pulses used 8-17

Representative conditions for printing a magenta image using this preferred thermal imaging member described above are as follows. Thermal printing head parameters:

-   Pixels per inch: 300 -   Resistor size: 2×(31.5×120) microns (split resistor) -   Resistance: 3000 Ohm -   Glaze Thickness: 200 microns -   Pressure: 3 lb/linear inch -   Dot pattern: Slanted grid.

The magenta color-forming layer is printed as shown in the table below. The line cycle time is divided into individual pulses of 7.14% duty cycle. The thermal imaging member is preheated by contact with the thermal printing head glaze at the heat sink temperature over a distance of about 0.3 mm.

Magenta printing Heat sink 30° C. temperature Dpi 300 (transport direction) Voltage 38 Line speed 0.75 inch/sec Pulse 131 microsec interval # pulses used 20-30

Representative conditions for printing a cyan image using this preferred thermal imaging member described above are as follows. Thermal printing head parameters:

-   Pixels per inch: 300 -   Resistor size: 2×(31.5×180) microns (split resistor) -   Resistance: 3000 Ohm -   Glaze Thickness: 200 microns -   Pressure: 3 lb/linear inch -   Dot pattern: Slanted grid.

The cyan color-forming layer is printed as shown in the table below. The line cycle time is divided into individual pulses of about 4.5% duty cycle. The thermal imaging member is preheated by contact with the thermal printing head glaze at the heat sink temperature over a distance of about 0.3 mm.

Cyan printing Heat sink 50° C. temperature Dpi 300 (transport direction) Voltage 38 Line speed 0.2 inch/sec Pulse 280 microsec interval # pulses used 33-42

Referring now to FIG. 1, a second preferred thermal imaging member 10 according to the invention is shown in schematic form. All layers were coated from aqueous fluids which contained small amounts of a coating aid, Zonyl FSN, available from Dupont Co., Wilmington, Del.

The substrate 12 is a filled, white, oriented polypropylene base of thickness about 200 microns, FPG200, available from Yupo Corporation America, Chesapeake, Va. 23320.

An adhesion-promoting layer 14 overlies the substrate 12, composed of the CP655 (a latex available from Dow Chemical Co., Midland, Mich., 48% by weight), CP692 (a latex available from Dow Chemical Co., Midland, Mich., 31% by weight) and POVAL MP103 (a fully hydrolyzed poly(vinyl alcohol) available from Kuraray America, Inc., New York, N.Y., 21% by weight). This layer has a coverage of 7.5 g/m².

Overlying the adhesion-promoting layer 14 is an oxygen barrier layer 16 composed of the above-mentioned POVAL MP103 (89.3% by weight) and glyoxal (a crosslinker, 10.7% by weight). This layer has a coverage of 1.2 g/m².

Overlying the oxygen barrier layer 16 is a cyan color-forming layer 18 composed of a cyan color-former having melting point 210° C., dye X of the present invention, 1,2-bis(2,4-dimethylphenoxy)ethane (a thermal solvent having melting point 112° C., coated as an aqueous dispersion of crystals having average particle size under 1 micron, 6 parts by weight), a phenolic antioxidant/developer (Anox 29, having melting point 161-164° C., available from Great Lakes Chemical Co., West Lafayette, Ind., coated as an aqueous dispersion of crystals having average particle size under 1 micron, 1 part by weight), Lowinox 1790 (a second phenolic antioxidant/stabilizer, available from Great Lakes Chemical Co., West Lafayette, Ind., coated as an aqueous dispersion of crystals having average particle size under 1 micron, 1.5 parts by weight), a binder (poly(vinyl alcohol), Celvol 205, available from Celanese, Dallas, Tex., 7 parts by weight) and glyoxal (0.42 parts by weight). This layer has a coverage of 3.35 g/m².

Overlying the cyan color-forming layer 18 is a barrier layer 20 that contains a fluorescent brightener. This layer is composed of the above-mentioned POVAL MP103 (82% by weight), glyoxal (8% by weight) and Leucophor BCF P115 (a fluorescent brightener, available from Clariant Corp., Charlotte, N.C., 10% by weight). This layer has a coverage of 2 g/m².

Overlying the barrier layer 20 is a thermally-insulating interlayer 22 composed of the above-mentioned CP692(40% by weight) and the above-mentioned CP655 (60% by weight). This layer has a coverage of 21 g/m².

Overlying the thermally-insulating interlayer 22 is a barrier layer 24 composed the above-mentioned POVAL MP103 (94% by weight) and glyoxal (a crosslinker, 6% by weight). This layer has a coverage of 1.5 g/m².

Overlying the barrier layer 24 is a magenta color-forming layer 26, composed of a magenta color-former, Dye IV described in U.S. patent application Ser. No. 11/433808, filed May 12, 2006, having a melting point of 152° C. (1 part by weight); a phenolic antioxidant/developer (Anox 29, having melting point 161-164° C., available from Great Lakes Chemical Co., West Lafayette, Ind., coated as an aqueous dispersion of crystals having average particle size under 1 micron, 3 parts by weight), Lowinox 1790 (a second phenolic antioxidant/stabilizer, available from Great Lakes Chemical Co., West Lafayette, Ind., coated as an aqueous dispersion of crystals having average particle size under 1 micron, 1 part by weight), a binder (poly(vinyl alcohol, Celvol 540, available from Celanese, Dallas, Tex., 3.2 parts by weight) and glyoxal (0.19 parts by weight). This layer has a coverage of 2.38 g/m².

Overlying the magenta color-forming layer 26 is a barrier layer 28 that contains a fluorescent brightener. This layer is composed of the above-mentioned POVAL MP103 (82% by weight), glyoxal (8% by weight) and the above-mentioned Leucophor BCF P115. This layer has a coverage of 1 g/m².

Overlying the barrier layer 28 is a second thermally-insulating interlayer 30 composed of the above-mentioned CP655 (48% by weight), the above-mentioned CP692 (31% by weight) and the above-mentioned POVAL MP103 (21% by weight). This layer has a coverage of 3 g/m².

Overlying the second thermally-insulating interlayer 30 is a barrier layer 32 composed the above-mentioned POVAL MP103 (94% by weight) and glyoxal (a crosslinker, 6% by weight). This layer has a coverage of 1 g/m².

Overlying the barrier layer 32 is a yellow color-forming layer 34 composed of Dye XI (having melting point 202-203° C.) described in U.S. Pat. No. 7,279,264, (59.6% by weight), Lowinox 1790 (a phenolic antioxidant/stabilizer, available from Great Lakes Chemical Co., West Lafayette, Ind., coated as an aqueous dispersion of crystals having average particle size under 1 micron, 7.6% by weight), a binder (poly(vinyl alcohol), Celvol 540, available from Celanese, Dallas, Tex., 32.8% by weight). This layer has a coverage of 1.99 g/m².

Overlying the yellow color-forming layer 34 is a barrier layer 36 composed of a fully hydrolyzed poly(vinyl alcohol), Celvol 325, available from Celanese, Dallas, Tex. (94% weight) and glyoxal (6% by weight). This layer has a coverage of 0.5 g/m².

Deposited on the barrier layer 36 is an ultra-violet blocking layer 38 composed of a nanoparticulate grade of titanium dioxide (MS-7, available from Kobo Products Inc., South Plainfield, N.J., 62% by weight), the above-mentioned POVAL MP103 (35% by weight) and glyoxal (3% by weight). This layer has a coverage of about 2 g/m².

Deposited on the ultra-violet blocking layer 38 is an overcoat 40 composed of a latex (CR-717, available from Lubrizol Co., Wickliffe, Ohio, 34% by weight), a styrene/maleic acid copolymer (SMA 1000MA, available from Sartomer Company, Wilmington, Pa., 6% by weight), the above-mentioned POVAL MP103 (5% by weight), a rheology modifier (Rheolate 310, available from Elementis Specialties, Inc, Hightstown, N.J., 3% by weight), a crosslinker (Bayhydur VPLS 2336, available from BayerMaterialScience, Pittsburgh, Pa., 34% by weight), zinc stearate (a meltable lubricant, available from Ferro Co., Cleveland, Ohio, 18% by weight). This layer has a coverage of 1 g/m².

On the reverse side of substrate 12 is an anticurl layer 42 comprising gelatin, of coverage 5 g/m².

The imaging members described above can be printed using techniques such as those described in U.S. Pat. No. 6,801,233, U.S. patent application Ser. No. 11/400734, filed Apr. 6, 2006, U.S. patent application Ser. No.. 11/400735, filed Apr. 6, 2006, and United States patent application Ser. No. ______, entitled “Print Head Pulsing Techniques for Multicolor Printers” of even date herewith.

The invention will now be described further in detail with respect to specific embodiments by way of an example, it being understood that this is intended to be illustrative only and the invention is not limited to the materials, amounts, procedures and process parameters, etc. recited herein. All parts and percentages recited are by weight unless otherwise specified.

Example XI

Synthesis of 4-methylacetanilide

A 22 L flask immersed in a water bath (25 C) was charged with p-toluidine (2.5 kg, 23.4 mole) in acetonitrile (8 L). Acetic anhydride (2.5 kg, 24.5 mole) added over -2 hours. During the addition the product crystallized and the batch temperature rose to ˜45 C. The batch was allowed to cool to ambient temperature overnight. The product was filtered off, washed with water and dried yielding a white solid (2.7 kg, 18.1 mole, 77%). A second crop of 200-300 g was obtained from the filtrate (˜3:1 water:acetonitrile). This material was characterized by NMR spectroscopy.

Synthesis of N-Methallyl-4-methylacetanilide

A 2 L reactor with batch temperature control was charged with 4-methylacetanilide (149 g, 1 mole), potassium hydroxide pellets (87%, 100 g,) in dimethylsulfoxide (650 mL) at 35 C. 3-Chloro-2-methyl-propene (90%, 112.7 g , 1.12 moles) was charged over 60 min holding the batch at 35 C. HPLC indicates complete reaction after 3 h. Water (600 mL) and heptane (200 mL) were added to the reactor. The lower layer was separated and discarded. The organic layer was washed with water (2×200 ml) then distilled to remove residual water (104 C pot temperature). Approximately 50 ml of water was removed. This yielded 278.5 g product of 67.6 wt % (188.2 g, 92.6% yield). This mixture was then used directly in the next step.

Synthesis of N-Acetyl-3,3,5-trimethylindoline

A 2 L reactor with batch temperature control was charged with aluminum chloride (340 g) and chlorobenzene (350 mL) and held at 80 C. N-methallyl-4-methylacetanilide (188.2 g heptane/chlorobenzene solution from the preceding step) was added over approximately one hour holding the batch at 80 C. The batch was held at 80 C for 2 hours. The batch was cooled to 25 C then quenched into a mixture of toluene (500 mL) and water (1400 mL). The aqueous layer was removed and the milky organic layer was washed with 6M HCl (2×200 ml) resulting in a clear green solution. This solution of N-Acetyl-3,3,5-trimethylindoline is used directly in the next step.

Synthesis of 3,3,5-trimethylindoline

The N-Acetyl-3,3,5-trimethylindoline solution from the previous step was returned to the 2 L reactor. Hydrochloric acid (6M, 500 mL) was added and the batch was held at reflux (97 C batch, 101 jacket) overnight. The batch was cooled to 70 C and the aqueous layer containing the product was collected. Crystals of the indoline HCl-salt form upon further cooling of the aqueous solution. The resulting suspension was treated with 456 NaOH (300 mL) bringing the pH to >10. Hexane (100 mL) was added to facilitate the phase split. The organic layer was separated, washed with water then concentrated under reduced pressure yielding crude 3,3,5-trimethylindoline (134 g) as a dark oil. The crude indoline was vacuum distilled yielding a colorless liquid (116 g, by ˜110 @ 3 mm, 78% yield from N-Methallyl-4-methylacetanilide). The structure and purity were confirmed by NMR spectroscopy and HPLC.

Synthesis of 3′-(3,3,5-trimethylindolino)-6′-chloro-4,5,6,7-tetrafluorofluoran

In a 12 liter flask was added sulfolane (3500 mL) followed by 3′,6′-Dichloro-4,5,6,7-tetrafluorofloran (826 g, 1.872 mole) and stirred. Aluminum chloride (1248 g, 9.36 mole) was added next in portions to keep the temperature under control. The temperature was allowed to reach 80 C and addition of the 3,3,5-trimethylindoline (300 g, 1.872 mole) was started with an addition funnel into the center of the vortex. After the 3,3,5-trimethylindoline was added, 2,6-lutidine (401 g, 3.744 mole) was similarly added. The reaction was allowed to stir for 30 minutes at temperature (70-80 C) then cooled. The warm reaction mixture (60 C) was poured into ice water (40 L) with rapid stirring. The light blue solid was collected by vacuum filtration, then washed with additional water (10 L) until the eluent, for all intents and purposes, became colorless.

The flocculent solid was washed with acetonitrile (2×2 L). The acetonitrile removed the water entrained in the solid, reduced the volume by 50% , and removed some of the dark blue impurities giving a pale blue product.

The solid was re-suspended in of acetonitrile (6.5 L) and heated. As heating proceeds, the suspended solid swells and thickens. The stirring rate must be increased to enable adequate stirring. After stirring at reflux for 15 minutes, the suspension was allowed to cool overnight to ambient temperature. The solid was collected by vacuum filtration, and washed with cold acetonitrile until the eluent was essentially colorless. The solid was dried overnight in a vacuum oven at 80 C (1013 g, 1,80 mole, 96%).

Synthesis of 3′-(3,3,5-trimethylindolino)-6′-(2,4-dimethylanilino)-4,5,6,7-tetrafluorofluoran

Diethylene glycol dimethyl ether (800 mL) was placed in a 2-L 3-necked flask and heating commenced. Anhydrous zinc chloride (117.7 g, 0.885 mole) was added but even after 1 hour of stirring at 120 C it had not dissolved completely. One equivalent of 2,4-dimethylaniline (21 g, 0.177 mole) was added. The solution typically turns pale brown and all the zinc chloride dissolves. 3′-(3,3,5-trimethylindolino)-6′-chloro-4,5,6,7-tetrafluorofloran (100 g, 0.177 mole) was added next as fast as it would dissolve. After stirring at 120 C for 30 minutes, a second equivalent of 2,4-dimethylaniline (21 g, 0.177 mole) was added and the temperature raised to 138 C. The blue solution was sampled for HPLC analysis after 4 hours at 138 C and found to be 1:1 starting material to product - none of the fluorine displacement by-product was visible by HPLC. A third equivalent of the aniline (21 g, 0.177 mole) was added and the reaction was again sampled after 5.5 hours. Analysis showed 70% completion. The remaining ½ equivalent of the aniline (10.5 g, 0.088 mole) was added and the reaction was allowed to continue overnight. After 16 hours, the dye formation was complete with very little unreacted starting material or side products. The reaction was allowed to cool to ˜60 C then poured into 4-liters of rapidly stirring ice water with 50 mL of concentrated hydrochloric acid added. A dark, blue-black solid separated out. After stirring for 30 minutes, the solid was collected by vacuum filtration. The solid was washed with additional water (2 L). The wet cake (529 g) was then dissolved in ethyl acetate (3.0 L). Once a solution was achieved, a 10% by weight aqueous solution of sodium acetate (1.0 L) was added and allowed to stir for 30 minutes. The stirring was stopped and the aqueous portion was removed. The aqueous sodium acetate extraction was repeated a total of two times (2×1.0 L) followed by extraction with water (2×1.0 L). The final phase split was allowed to settle overnight before the water was removed. If the phase split does not occur, the amount of ethyl acetate that the dye is dissolved in must be increased. The ethyl acetate/water azeotrope was distilled off until nearly 1.5 liters of solution had been removed (some loss due to evaporation). The remainder was then transferred into a smaller vessel and distillation was continued. Another 1000 mL of solution was removed, leaving about 500 mL in the vessel. The solution in the pot now took on a purple-blue color. Heptane was added (750 mL), as well as a few seed crystals. The distillation was continued until solid was visible in the stirrring solution; (an additional 100 mL of EtOAc distilled over). Once solid was visible, heating was stopped and the suspension allowed to cool to RT. The solid was collected and washed with heptane, dried overnight in a vacuum oven at 60 C. Dried recovery =89.4 g. This was dissolved in 200 mL of boiling chlorobenzene. The initial color of the solution of dye was blue, but as the residual water azeotropes off (just a few minutes) the solution turn purple. Heptane (450 mL) was then poured slowly into the boiling solution - the addition is such that the reflux of solvent is never allowed to stop; a few seed crystals were also added. Once all of the heptane had been added, heating was stopped, and the solution allowed to cool to RT. Solid began precipitating out nearly as soon as heating is stopped. The solid is collected, washed with cold 20% Chlorobenzene/Heptane, followed by heptane alone. The solid was dried in a vacuum oven at 60 C overnight. (Yield: 76 g, 0.117 mole, 66%). The color of the material was a pale blue and the purity by HPLC was 97% by weight. The dye was characterized by mass spectrometry, DSC-TGA and NMR spectroscopy.

Although the invention has been described in detail with respect to various preferred embodiments, it is not intended to be limited thereto, but rather those skilled in the art will recognize that variations and modifications are possible which are within the spirit of the invention and the scope of the appended claims. 

1. A thermal imaging member comprising a substrate carrying an image-forming layer which includes a compound represented by the formula I:

wherein: R₁, R₃, R₄, R₅, R₆ and R₇ are each independently selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted, alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, halogen, nitro, nitrilo, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, oxygen, substituted oxygen, nitrogen, substituted nitrogen, sulfur and substituted sulfur; R₂ is selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, substituted oxygen, substituted nitrogen and substituted sulfur; R₈ is absent or selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, halogen, nitro, nitrilo, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, oxygen, substituted oxygen, nitrogen, substituted nitrogen, sulfur and substituted sulfur; R₉, R₁₀ and R₁₁ are independently selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, halogen, nitro, nitrilo, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, oxygen, substituted oxygen, nitrogen, substituted nitrogen, sulfur and substituted sulfur; R₁₂, R₁₃, R₁₄ and R₁₅ are independently selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, aryl, substituted aryl, heteroaryl, and substituted heteroaryl; R₁₆, R₁₇, R₁₈ and R₁₉ are independently selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, halogen, nitro, nitrilo, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, oxygen, substituted oxygen, nitrogen, substituted nitrogen, sulfur and substituted sulfur; and X₁ is carbon or nitrogen; wherein said compound is in the crystalline form.
 2. The thermal imaging member as defined in claim 1 wherein said compound represented by formula I has a glass transition temperature of at least 50° C.
 3. The thermal imaging member as defined in claim 1 wherein said image-forming layer further comprises at least one thermal solvent.
 4. The thermal imaging member as defined in claim 3 wherein said thermal solvent is selected from the group consisting of diphenylsulfone, 4,4′-dimethyldiphenylsulfone, phenyl p-tolylsulfone, 4,4′-dichlorodiphenylsulfone, 1,2-bis(2,4-dimethylphenoxy)ethane, 1,4-bis(4-methylphenoxymethyl)benzene, 1,4-bis(benzyloxy)benzene and mixtures thereof.
 5. The thermal imaging member as defined in claim 1 wherein said image-forming layer further comprises at least one compound comprising a phenolic grouping.
 6. The thermal imaging member as defined in claim 5 wherein said compound comprising a phenolic grouping is selected from the group consisting of 2,2′-methylenebis(6-tert-butyl-4-methylphenol), 2,2′-methylenebis(6-tert-butyl-4-ethylphenol), 2,2′-ethylidenebis(4,6-di-tert-butylphenol), bis[2-hydroxy-5-methyl-3-(1-methylcyclohexyl)phenyl]-methane, 1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl)isocyanurate, 2,6-bis[[3-(1,1-dimethylethyl)-2-hydroxy-5-methylphenyl]methyl]-4-methylphenol, 2,2′-butylidenebis[6-(1,1-dimethylethyl)-4-methylphenol, 2,2′-(3,5,5-trimethylhexylidene)bis[4,6-dimethyl-phenol], 2,2′-methylenebis[4,6-bis(1,1-dimethylethyl)-phenol, 2,2′-(2-methylpropylidene)bis[4,6-dimethyl-phenol], 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, 2,2′-thiobis(4-tert-octylphenol), and 3-tert-butyl-4-hydroxy-5-methylphenyl sulfide.
 7. A thermal imaging method comprising (a) providing an imaging member as defined in claim 1; and (b) converting at least a portion of said compound to an amorphous form in an image-wise pattern whereby an image is formed.
 8. The thermal imaging method as defined in claim 7 wherein step (b) comprises applying an image-wise pattern of thermal energy to said imaging member, said thermal energy being sufficient to convert at least some of said compound to an amorphous form.
 9. A compound of formula I

in which: R₁, R₃, R₄, R₅, R₆ and R₇ are each independently selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted, alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, halogen, nitro, nitrilo, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, oxygen, substituted oxygen, nitrogen, substituted nitrogen, sulfur and substituted sulfur; R₂ is selected from the group consisting of aryl, and substituted aryl; R₈, R₉, R₁₀ and R₁₁ are fluorine atoms; R₁₂ and R₁₃ are hydrogen atoms; R₁₄ and R₁₅ are identical substituents selected from the group consisting of alkyl having from 1 to 18 carbon atoms and substituted alkyl having from 1 to 18 carbon atoms; R₁₆, R₁₇, R₁₈ and R₁₉ are independently selected from the group consisting of hydrogen, alkyl, preferably having from 1 to 18 carbon atoms, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, heterocycloalkyl, substituted heterocycloalkyl, substituted carbonyl, acylamino, halogen, nitro, nitrilo, sulfonyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, oxygen, substituted oxygen, nitrogen, substituted nitrogen, sulfur and substituted sulfur; and X₁ is carbon.
 10. The compound of formula I in which R₂ is a 2,4-dimethylphenyl group, R₈, R₉, R₁₀ and R₁₁ are fluorine, R₁₄, R₁₅ and R₁₇ are methyl groups, R₁, R₃, R₄, R₅, R₆, R₇, R₁₂, R₁₃, R₁₆, R₁₈ and R₁₉ are hydrogen and X₁is carbon. 